[
    {
        "id": 1,
        "chunk": "# Black Phosphorus/Polymers: Status and Challenges  \n\nYe Zhang, Chunyang Ma, Jianlei Xie, Hans Ågren,\\* and Han Zhang\\*  \n\nAs a newly emerged mono-elemental nanomaterial, black phosphorus (BP) has been widely investigated for its fascinating physical properties, including layer-dependent tunable band gap (0.3–1.5 eV), high ON/OFF ratio $(70^{4})$ , high carrier mobility $(70^{3}\\mathsf{c m}^{2}\\mathsf{V}^{-1}\\mathsf{s}^{-1})$ , excellent mechanical resistance, as well as special in-plane anisotropic optical, thermal, and vibrational characteristics. However, the instability caused by chemical degradation of its surface has posed a severe challenge for its further applications. A focused BP/polymer strategy has more recently been developed and implemented to hurdle this issue, so at present BP/polymers have been developed that exhibit enhanced stability, as well as outstanding optical, thermal, mechanical, and electrical properties. This has promoted researchers to further explore the potential applications of black phosphorous. In this review, the preparation processes and the key properties of BP/polymers are reviewed, followed by a detailed account of their diversified applications, including areas like optoelectronics, bio-medicine, and energy storage. Finally, in accordance with the current progress, the prospective challenges and future directions are highlighted and discussed.  \n\nhave still not been realized owing to the intrinsic lack of a band gap, something that has greatly limited its applications in the field of semiconductor devices.[2] Transition metal disulfides (TMDs) are a series of other extensively studied 2D vdW materials, especially the most famous one— $\\mathrm{MoS}_{2}$ , which possesses a similar structure to graphene and exhibits direct band gaps when its thickness is reduced to a monolayer.[3] However, due to its relatively low carrier mobility there is difficulty in meeting the preparation requirements of next-generation optoelectronic devices.[4]  \n\nPhosphorus, an abundant group V element on Earth, mainly exhibits three forms of allotropes: White phosphorus (WP), red phosphorus (RP), and black phosphorus (BP).[5] Among them, BP has the most stable structure and is insoluble in most solvents, it is non-flammable and has the lowest chemical reaction energy at normal temperature and pressure.[6]",
        "category": " Introduction"
    },
    {
        "id": 2,
        "chunk": "# 1. Introduction  \n\nFollowing the first successful exfoliation of graphene from graphite in the 20th century, 2D layered van der Waals (vdW) nanomaterials have aroused wide attention and led to a rapid development of 2D layered vdW-based devices owing to their fantastic structural and physical properties.[1] Nevertheless, despite extensive research, logic circuit switches using graphene  \n\nBP has been considered as a newly emerging star of 2D vdW semiconductor materials since its first appearance in 2014.[6c,7] The fascinating properties of BP are in principal determined by its unusual structure, geometric and electronic.[8] Figure  1a–c shows an atomic ball-stick schematic of a few-layer BP with typical fold structure due to the $\\displaystyle\\mathrm{sp}^{3}$ orbital hybridization, where special armchair- and zigzag-shapes can be observed along the $x\\cdot$ and $\\gamma$ -axial directions, respectively, resulting in an asymmetry of BP and in specific in-plane anisotropic characteristics of its optical, thermal, and electronical properties.[9] In particular, every $\\mathrm{\\DeltaP}$ atom is linked with two neighboring intraplane P atoms by covalent bonds, and every BP layer is stacked via weak vdW interactions. Comparing with the $220{-}350\\ \\mathrm{cm^{2}\\vee^{-1}\\ \\mathrm{s^{-1}}}$ hole mobilities of bulk BP, few-layer BP displays a hole mobility as high as $10^{3}\\ \\mathrm{cm}^{2}\\ \\mathrm{V}^{-1}\\ \\mathrm{s}^{-1}$ , which can match that of silicon (Si) at room temperature.[10] As shown in Figure  1d–f, BP has been proven to have a layer-dependent tunable direct-bandgap ranging from 0.3 (bulk) to $1.5\\ \\mathrm{eV}$ (monolayer), thereby exhibiting a wide optical absorption window of the solar spectrum that covers the ultraviolet (UV) to mid-infrared regime.[11] These extraordinary properties of BP give prospects for many new generation applications.  \n\nNevertheless, the degradation of the surface of BP is still a serious challenge that needs to be solved so as to effectively enhance the long-term stability of BP devices.[13] It follows that great efforts have been undertaken to bring light on the degradation mechanism of BP by experimental as well as theoretical research. Results of photooxidation of multilayer BP through AFM analysis and theoretical calculations are depicted in Figure  2.[14] The generally adopted degradation mechanism is the synergetic effect of light illumination, water, and oxygen. A three-step degradation process of BP has been presented, including the formation of superoxide, the formation of phosphate, and the breaking of the top layer. Finding appropriate strategies to slow down the degradation rate and improve the environmental stability of BP has thus become a long term pursuit for researchers. As shown in Figure 3 various technologies have been proposed to passivate BP, such as, surface functional modification,[15] adsorption of heavy metal cations,[16] introduction of stable protective layers,[8c,17] fluorination,[18] and incorporation with different polymers.[19]  \n\n![](images/452cb67bf8f487d368b729d8acb3e7425c2b903ad22f7786eea4674075efb6c0.jpg)  \nFigure 1.  a) Atomic ball-stick schematic of few-layer BP. b) Top view. c) Side view. d,e) Band structures of monolayer and bilayer BP calculated throug the HSE06 methods. f) The relationship of band gaps versus thickness of BP. a–c) Reproduced with permission.[8a] Copyright 2017, Royal Society of Chemistry. d–f) Reproduced with permission.[11d] Copyright 2014, Springer Nature.  \n\nThe development of BP passivation technologies has greatly improved the stability of BP. Among the reported passivation technologies, the incorporation of BP with polymers has been considered as the most promising strategy, ascribing to advantages like low cost, easy fabrication process, nontoxicity, and environmentally friendliness.[12d,22] Recently achieved progress in studies of BP/polymers indicates a great potential for applications of optoelectronic devices,[23] bio-medical therapy,[24] and energy storage.[25] Up to now, with the burgeoning of BP/ polymers, most of the current reported BP/polymer reviews have been focused on bio-medical applications, while a more comprehensive and a systematic summarization of their preparation methods, properties, and applications is urgently in demand, which could be beneficial for the further design of novel BP/polymers with high-performance. With this statement as starting point, we here first introduce various fabrication approaches and properties of BP/polymers. This is followed by a discussion of their multiple applications in optoelectronics, energy/information storage, flame retardancy, bio-medical, and other potential applications. Finally, an outlook of prospects, opportunities, and challenges of BP/polymers in the future is presented. We believe that this review can bring new significance to the development of BP/polymers.",
        "category": " Introduction"
    },
    {
        "id": 3,
        "chunk": "# 2. Preparation of Black Phosphorus/Polymers  \n\nIn decades, polymers or named macromolecules have attracted an increasing research interest due to their rich advantages like easy fabrication and modification methods, low consumption, environmental friendliness, and flexibility in structure, which have been widely explored to combine with inorganic materials to form inorganic/polymers nanocomposites with some novel features, including enhanced mechanical, electronical, thermal, and stability properties.[26] Researchers have much utilized inorganic/polymers nanocomposites for applications in various fields such as catalysis, gas absorption, energy storage, environmental protection, and governance.[27]  \n\nBecause of the numerous active sites on the surface of BP and the easy fabrication and modification features of polymers, BP/polymer nanocomposites have been extensively investigated and can be prepared into various morphologies.[6a,25a,28] Additionally, BP has also been proved to be hydrophilic owing to its strong out of plane dipolar moment.[8a,8c,29] So far, lots of polymers, like PLGA, PU, PEG, PDA, PPy, PVA, and PANI, have been investigated to fabricate BP/polymer nanocomposites, where the components are connected with a relatively weak interaction including vdW forces, electrostatic binding, and hydrogen chemical bonds. To the best of our knowledge, the most adopted methods to prepare BP/polymers comprise solution casting (SC), polymerization methods (PMs), and spinning technology (ST) methods. Table 1 lists the preparation methods and applications of BP/polymer nanocomposites highlighted during the recent 6 years. It is noteworthy that the development of BP/polymer nanocomposites shows an increasing trend year by year and that the most adopted one is the solution casting (SC) method which covers over more than half of all the reported cases in the literature.  \n\n![](images/088610522d61879b1eab7055341f61ea41e50eab8feda1dd21dbe289f487e6da.jpg)  \nFigure 2.  a) AFM images of fresh BP and of BP placed for some days under ambient environment. b) The comparison of concentrations of $\\mathsf{P O}_{2}{}^{3-}$ , ${\\mathsf{P O}}_{3}^{3-}$ , and ${\\mathsf{P O}}_{4}^{3-}$ under ambient light. c) Mole fractions of ${\\mathsf{P O}}_{2}{}^{3-}$ , ${\\mathsf{P O}}_{3}{}^{3-}$ , and ${\\mathsf{P O}}_{4}^{3-}$ after different storage days. d) Oxidation kinetics of ${\\sf H}_{3}{\\sf P}{\\sf O}_{x}$ $\\left(_{x}=2,3\\right.$ , or 4) from the zigzag edge of BP. e) Theoretical degradation mechanism of BP under light illumination. a) Reproduced with permission.[13d] Copyright 2017, Springer Nature. b–d) Reproduced with permission.[20] Copyright 2018, American Chemistry Society. e) Reproduced with permission.[14b] Copyright 2016, Wiley-VCH.",
        "category": " Materials and methods"
    },
    {
        "id": 4,
        "chunk": "# 2.1. Solution Casting  \n\nAs discussed above, SC has become one of the most important ways to prepare BP/polymer nanocomposites since its first appearance in 1995.[116] The interaction between BP and polymers is strong owing to the special polar nature of both constituents, leading to an enhanced flexibility of the obtained membranes.[41,56,74,117] In a typical procedure, specific amounts of polymers and BP are dissolved in solvents to form homogeneous solutions with the assistance of sonication or vigorous stirring as shown in Figure  4. The BP/polymer membranes with well-defined composition can subsequently be obtained through filtration and evaporation at high temperatures to remove the extra solvents. Li et  al. obtained a membrane via introducing BP into a PVA matrix[46] and could demonstrate that the so prepared BP/PVA membrane shows an excellent flexibility with a significantly enhanced discharge capacity. Zhang’s group reported coated BP quantum dots (BP QDs) with polyionic liquid poly(1-hexyl-3-vinylimidazolium) hexa­ fluorophosphate salt (PIL-TFSI), followed by mixing the coated BP with PVDF and dropped onto a clean ITO glass under $80^{\\circ}$ to remove the solvent for fabricating a PEC-type photodetector with long-term stability.[23a] $\\mathrm{~In~}2019$ , Wan and coworkers first prepared a BP/graphite hybrid, followed by mixing the hybrid with PANI to prepare a ternary membrane through filtration.[70]  \n\n![](images/86529de51502264c5d3dd77bce0e331296ba58214d9a7f5daada2bd357e6df67.jpg)  \nFigure 3.  a) h-BN and graphene encapsulated BP. b) PDI molecules adsorbed BP. c) The adsorption of ${\\mathsf{A}}{\\mathsf{g}}^{+}$ on the surface of BP. d) Fluorination of BP with $\\mathsf{F}_{2}$ . e) PU polymer incorporated BP. a) Reproduced with permission.[17a] Copyright 2015, American Chemistry Society. b–d) Reproduced with perm ission. $[75d,76a,78a]$ Copyright 2016–2018, Wiley-VCH. e) Reproduced with permission.[21] Copyright 2018, Elsevier Ltd.  \n\nDifferent from the above introduction of preparing membranes with a large amount of polymers, surface functional modification is another popular SC method to prepare BP/ polymer nanocomposites with appropriate polymer additives.[73] Taking advantage of the hydrophilic nature of BP, lots of hydrophilic polymers have been explored to modify BP via the SC method. For example, hydrophilic functionalized PEG is one of the most commonly used polymers to fabricate nanocomposites with BP attributes to its advantage like good biocompatibility and physiological stability in media.[43,62,89] $\\mathrm{In}2015$ , BP QDs were first surface modified with PEG- $\\mathrm{\\cdotNH}_{2}$ by Zhang et al.[31] and were then dissolved in deionized water (DW) and sonicated for $30~\\mathrm{min}$ , so obtaining a BP/PEG- $\\mathrm{\\cdotNH}_{2}$ nanocomposite that was treated by repeated centrifugation and water rinsing. The BP/PEG- $\\mathrm{\\cdotNH}_{2}$ nanocomposite exhibits non-toxicity and enhanced physiological stability, and was demonstrated to be a promising photothermal agent for cancer therapy. In 2017, these authors further proposed that $\\mathrm{BP/PEG{\\cdot}N H_{2}}$ also could be a robust delivery platform for cancer theranostics. Yang’s group prepared near-infrared region/reactive oxygen species $\\left(\\mathrm{NIR}\\right/$ ROS) response BP/polymers by grafting with pyrene modified poly (propylene sulfide) and PEG, which was proposed to serve as an effective immunoadjuvant carrier for cancer therapy.[84] There are also lots of other hydrophilic PEGs adopted to prepare BP/polymers like BP/PEG-FA,[83] BP/PEG- $\\mathrm{\\cdotNH}_{2}/\\mathrm{Sgc}8$ ,[80] BP/PEG- $\\ensuremath{\\mathrm{\\cdotNH}}_{2I}$ /RdB,[45] BP/PEG/PPy.[82] In addition to the most explored PEGs, some other hydrophilic polymers have also been developed to fabricate BP/polymer nanocomposites. For example, PLL was mixed with BP NSs for biosensors with good catalytic activity.[47] Besides that, BP has also been reported as a promising material for optical applications through SC met hods.[28,33,39,49,118] Yun and coworkers found that the usage of BP NSs with PVA as saturable absorbers (SAs) can provide dualwavelength vector soliton mode locking in an erbium-doped fiber laser.[37] PDDA was applied to incorporate BP NSs via electrostatic interaction in solution by Zhao et  al.[51] They claimed that the PDDA can not only passivate the lone-pair electrons of P but also enhance its dispersity in water, showing that the prepared BP/PDDA film is a promising candidate for applications in ultrafast optics. Zhang’s group prepared a BP/PIL nanocomposite by mixing BP with -(PIL-TFSI).[23a] The prepared BP/PIL exhibited good photo-response behaviors, as well as excellent self-healable capability.  \n\nTable 1.  Articles on BP/polymers published from 2015 to 2021.   \n\n\n<html><body><table><tr><td>Year</td><td>BP/polymer</td><td>Method</td><td>Application</td><td>Ref</td></tr><tr><td>2015</td><td>BP/PMMA</td><td>ST</td><td> Laser technology</td><td>[30] </td></tr><tr><td rowspan=\"5\">2016</td><td>BP/PEG-NH2</td><td>SC</td><td>PTT</td><td>[31] </td></tr><tr><td>BP/PVP</td><td>SC</td><td>Information storage</td><td>[32]</td></tr><tr><td>BP/PC</td><td>Thermal evaporation</td><td>Laser technology</td><td>[33] </td></tr><tr><td>BP/PEODT:PSS</td><td>SC</td><td>-</td><td>[34]</td></tr><tr><td>BP/PLGA</td><td>SC </td><td>PTT</td><td>[35] </td></tr><tr><td rowspan=\"5\">2017</td><td>BP/PEG</td><td>Mechanical milling</td><td>PA imaging, PTT</td><td>[24b]</td></tr><tr><td>UCNP-PAA/BP-PEG</td><td>SC</td><td>PDT</td><td>[36] </td></tr><tr><td>BP/PVA</td><td>SC</td><td>Laser technology</td><td>[37]</td></tr><tr><td>BP/PVA</td><td>SC </td><td>Laser technology</td><td>[38] </td></tr><tr><td>BP/PDMS</td><td>PM</td><td>Laser technology</td><td>[39]</td></tr><tr><td rowspan=\"16\">2018</td><td>BP/PMMA</td><td>ST</td><td>Ultrafast photonics</td><td>[40] </td></tr><tr><td>BP/PMMA</td><td>PM</td><td>Information storage</td><td>[4] </td></tr><tr><td>BP/PAH</td><td>SC</td><td>siRNA delivery, PTT</td><td>[42]</td></tr><tr><td>BP/PEG-CA</td><td>SC </td><td> Fluorescence imaging</td><td></td></tr><tr><td>BP/PEG</td><td>SC</td><td>Drug delivery, PTT</td><td>[43]</td></tr><tr><td>BP/PEG</td><td>SC</td><td></td><td>[44] </td></tr><tr><td>BP/PVA</td><td>SC</td><td>Fluorescence imaging, PDT/PTT Zinc-nickel battery</td><td>[45] </td></tr><tr><td>BP/PANI</td><td>Electrochemical deposition</td><td>Supercapacitor</td><td>[46]</td></tr><tr><td>BP/CNT/TPU</td><td>ST</td><td>Supercapacitor</td><td>[25b] </td></tr><tr><td>BP/PLL</td><td>SC</td><td>Biosensor</td><td>[25c]</td></tr><tr><td>BP/PPy</td><td></td><td></td><td>[47]</td></tr><tr><td>BP/PVA</td><td>SC SC</td><td>Electron-sensor</td><td>[48]</td></tr><tr><td>BP/PVA</td><td>SC</td><td>Laser technology Laser technology</td><td>[49]</td></tr><tr><td>BP/PDDA</td><td>SC </td><td>Laser technology</td><td>[50] </td></tr><tr><td>BP/PDMS</td><td></td><td></td><td>[5]</td></tr><tr><td>BP/PMMA</td><td>PM</td><td> Laser technology</td><td>[52] </td></tr><tr><td>BP/PMMA</td><td>SC</td><td>Laser technology</td><td>[53] </td></tr><tr><td>BP/PTFE</td><td>PM</td><td></td><td>[54]</td></tr><tr><td>BP/PEDOT:PSS</td><td>SC</td><td></td><td>[55] </td></tr><tr><td>BP/PLGA</td><td>SC</td><td></td><td>[56] </td></tr><tr><td>BP/PDDF</td><td>ST</td><td></td><td>[5]</td></tr><tr><td>BP/PU</td><td>PM</td><td>Information storage</td><td>[58] </td></tr><tr><td>BP/PU</td><td>SC </td><td> Flame retardancy</td><td>[59]</td></tr><tr><td>BP/PDLLA/PEG/PDLLA</td><td>SC </td><td>Shape memory</td><td>[21]</td></tr><tr><td>BP/Agarose</td><td>PM</td><td>PTT, antibacterial</td><td>[60]</td></tr><tr><td>BP/C-PEG</td><td>PM</td><td> Drug delivery</td><td>[24c] </td></tr><tr><td>BP/PDA/PEG</td><td>SC</td><td> Drug and siRNA delivery, photoimmunotherapy</td><td>[6] </td></tr><tr><td>BP/PVA</td><td>SC freeze drying</td><td>Drug and siRNA delivery, PTT</td><td>[62]</td></tr><tr><td>BP/PLGA</td><td></td><td>Drug delivery</td><td>[63]</td></tr><tr><td>BP/PLGA/PEI</td><td>SC</td><td>Drug delivery, bone regeneration</td><td>[64]</td></tr><tr><td>BP/PPMS-EPO</td><td>SC</td><td>Tumor radiosensitization</td><td>[65] </td></tr><tr><td>BP/PEI</td><td>SC</td><td>Antibacterial</td><td>[66] </td></tr><tr><td></td><td>Mechanical milling</td><td> Bio-imaging</td><td>[67] [68] </td></tr><tr><td></td><td>BP/PEI</td><td>SC PM</td><td>PDT</td></tr><tr><td>2019</td><td>BP/Cellulose hydrogel</td><td>PTT</td><td>[69]</td></tr><tr><td>BP/PPy</td><td>PM</td><td>Supercapacitor</td><td>[25d] </td></tr><tr><td>BP/G/PANI</td><td>SC</td><td>Na-ion battery</td><td>[70] </td></tr><tr><td>BP/PS/PAA</td><td>SC</td><td>Biosensor</td><td>[7]</td></tr></table></body></html>  \n\nTable 1. Continued.   \n\n\n<html><body><table><tr><td>Year</td><td>BP/polymer</td><td>Method</td><td>Application</td><td>Ref</td></tr><tr><td></td><td>BP/PP</td><td>SC</td><td>Biosensor</td><td>[72] </td></tr><tr><td></td><td>BP/PDDA</td><td>SC</td><td>Biosensor</td><td>[73]</td></tr><tr><td></td><td>BP/PVDF</td><td>SC</td><td>Photodetector</td><td>[23a] </td></tr><tr><td></td><td>BP/PVDF</td><td>SC</td><td></td><td>[74]</td></tr><tr><td></td><td>BP/PFCz-NH2</td><td>PM</td><td>Information storage</td><td>[75] </td></tr><tr><td></td><td>BP/PZN</td><td>PM</td><td>Flame retardancy</td><td>[76]</td></tr><tr><td></td><td>BP/PU</td><td>PM</td><td>Flame retardancy</td><td>[77]</td></tr><tr><td></td><td>BP/Pluronic F-127</td><td>Cold method</td><td>Drug delivery, PTT</td><td>[78]</td></tr><tr><td></td><td>BP/PLGA</td><td>SC</td><td>Drug delivery, PTT</td><td>[79]</td></tr><tr><td></td><td>BP/PEG</td><td>SC</td><td>Drug delivery, PTT</td><td>[80] </td></tr><tr><td></td><td>BP/PDA/PEG</td><td>SC</td><td>Drug delivery, PTT/PDT</td><td>[81] </td></tr><tr><td></td><td>BP/PPy</td><td>SC</td><td>PTT</td><td>[82]</td></tr><tr><td></td><td>BP/PEG-FA</td><td>SC</td><td>Drug delivery, PTT</td><td>[83] </td></tr><tr><td></td><td>BP/Pyrene-PEG</td><td>SC</td><td>PDT</td><td>[84]</td></tr><tr><td></td><td>BP/PCL</td><td>ST </td><td>Bone regeneration</td><td>[85] </td></tr><tr><td></td><td>BP/PEA/GelMA</td><td>PM</td><td>Bone regeneration</td><td>[86] </td></tr><tr><td></td><td>BP/PEG</td><td>SC</td><td>Drug delivery, PTT</td><td>[87]</td></tr><tr><td></td><td>BP/PCL</td><td>SC</td><td>Tissue regeneration</td><td>[88]</td></tr><tr><td></td><td>BP/PEG-FA/PAH</td><td>SC</td><td>Bio-imaging, PDT</td><td>[89]</td></tr><tr><td></td><td>BP/PHEA/PDMA</td><td>PM</td><td>Bone regeneration</td><td></td></tr><tr><td></td><td>BP/PEG</td><td>SC</td><td>PDT</td><td>[90] </td></tr><tr><td></td><td>BP/PDA</td><td>PM</td><td>PTT/PDT</td><td>[91] </td></tr><tr><td>2020</td><td>BP/PANI</td><td>PM</td><td>Na-ion battery</td><td>[92] </td></tr><tr><td>BP/PI</td><td></td><td>PM</td><td></td><td>[93]</td></tr><tr><td>BP/PU</td><td></td><td>SC</td><td>Flame retardancy</td><td>[94]</td></tr><tr><td>BP/PU</td><td></td><td></td><td>Flame retardancy</td><td>[95]</td></tr><tr><td>BP/EP</td><td></td><td>SC PM</td><td>Flame retardancy</td><td>[96] </td></tr><tr><td>BP/MCNT/EP</td><td></td><td>PM</td><td>Flame retardancy</td><td>[97]</td></tr><tr><td>BP/(CFSO3)3Er/EP</td><td></td><td>PM</td><td>Flame retardancy</td><td>[98] </td></tr><tr><td></td><td>BP/graphite oxide/EP</td><td>PM</td><td>Flame retardancy</td><td>[99]</td></tr><tr><td>BP/PVA/PDA</td><td></td><td>PM</td><td>Flame retardancy</td><td>[100] [101] </td></tr><tr><td>BP/PEI/PUA</td><td></td><td>PM</td><td>Flame retardancy</td><td>[102] </td></tr><tr><td></td><td>BP/COF</td><td>solvothermal</td><td> Flame retardancy</td><td></td></tr><tr><td></td><td>BP/PLLA/PEG/PLLA</td><td>SC</td><td>Drug delivery, PTT</td><td>[103] [104]</td></tr><tr><td></td><td>BP/PLGA</td><td>SC</td><td>PTT</td><td>[105] </td></tr><tr><td></td><td>BP/PLGA</td><td>PM</td><td>Rheumatoid arthritis therapy</td><td>[106]</td></tr><tr><td></td><td>BP/PLGA</td><td>Cryogenic environment</td><td>Drug delivery, PTT, bone generation</td><td>[107]</td></tr><tr><td></td><td>BP/PLL</td><td>SC</td><td>Cas13a/crRNA delivery</td><td>[108]</td></tr><tr><td></td><td>BP/PLCL/Laminin</td><td>ST</td><td>Neuritogenesis</td><td>[109]</td></tr><tr><td></td><td>BP/G/PANI</td><td>SC</td><td>Li-ion battery</td><td>[110] </td></tr><tr><td>2021 BP/TPU</td><td></td><td>PM</td><td>Flame retardancy</td><td>[11]</td></tr><tr><td>BP/graphene/TPU</td><td></td><td></td><td></td><td></td></tr><tr><td>BP/PEG</td><td></td><td>PM</td><td>Flame retardancy PDT/PTT/photoimmunotherapy</td><td>[112] </td></tr><tr><td>BP/Cys-PDSA</td><td></td><td>SC Nanoprecipitation</td><td>Bioimaging,drug delivery</td><td>[113] [114]</td></tr></table></body></html>\n\nPDT: Photodynamic therapy, PTT: Photothermal therapy, PAA: Polyacrylic acid, PANI: Polyaniline, PAH: Poly(allylamine hydrochloride), PC: Polycarbonate, PCL: Poly(ε- caprolactone), PDDA: Poly(diallyldimethylammonium chloride), PDDF: Poly[(1,4-diethynylbenzene)-alt-9,9-bis(4-diphenylaminophenyl)fluorene], PDLLA: Poly(d,l-lactide), PDMA: Poly(N,N-dimethyl acrylamide), PDMS: Polydimethylsiloxane, PDSA: Poly-(disulfide amide), PEA: Poly(ester amide)s, PEDOT:PSS: Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate, PEG: Polyethylene glycol, PEI: Polyethylenimine, ${\\mathsf{P F C z}}{\\mathsf{-N H}}_{2}$ : Poly[(9,9-dioctyl-9H-fluorene)-alt-(4-(9H-carbazol-9-yl)aniline)], PHEA: poly(2-hydroxyethylacrylate), PI: Polyimide, PLCL: poly(L-lactide-co-ε-caprolactone), PLGA: Poly(lactic-co-glycolic acid), PLL: Poly-L-lysine, PLLA: Poly(L-lactide), PMMA: Poly (4-pyridonemethylstyrene), PP: Polypeptide, $\\mathsf{P P y}\\mathrm{:}$ Polypyrrole, PPMS-EPO: poly (4-pyridonemethylstyrene) endoperoxide, PTFE: Polytetrafluoroethylene, PU: Polyurethane, PVA: Poly(vinyl alcohol), PVDF: Polyvinylidene fluoride, PVP: Polyvinyl pyrrolidone, PZN: Polyphosphazene, TPU: Thermoplastic polyurethane.  \n\n![](images/10a0443a632c30c4bf32fbac60565f9bdca33334f0ef61edb50f2b4070d67650.jpg)  \nFigure 4.  a–c) Preparation of BP/polymers via SC methods. d,e) SEM and TEM images of prepared BP/PEG. f) Elements mapping of prepared BP/ polymers. a,b) Reproduced with permission.[19a,84] Copyright 2015 and 2018, Wiley-VCH. c) Reproduced with permission.[115] Copyright 2018, The Royal Society of Chemistry. d–f) Reproduced with permission.[72,79] Copyright 2017 and 2019, American Chemistry Society.  \n\nAnother most used SC method is the emulsion solvent evaporation method, often named as the oil-in-water emulsion solvent evaporation method.[64,71,72,105,107,119] In a typical procedure using this method, materials are first dispersed in organic solvents to form a homogeneous solution, which subsequently is added into an aqueous solution and sonicated to obtain the emulsion. Finally, the BP/polymer nanocomposites are obtained by centrifugation. For example, Chu et  al. first dissolved BP QDs and PLGA in dichloromethane (DCM), and added the mixture in PVA aqueous solution and stirred it overnight to remove residual DCM at room temperature. The BP/ PLGA suspension was first centrifuged for several minutes, and then the product was washed with deionized water.[35] They proved that such prepared BP/PLGA can prevent the rapid degradation of BP and give a highly efficient photothermal performance. Chen et al. first uniformly dispersed BP and PLGA in acetone through ultrasonication followed by dropping the organic phase in an aqueous solution. (PEI) polyetherimide was then transferred into the solution and stirred overnight to prepare a BP/PLGA/PEI nanocomposite for precise tumor radiosensitization.[65]",
        "category": " Materials and methods"
    },
    {
        "id": 5,
        "chunk": "# 2.2. Polymerization Method  \n\nPM is a mainly adopted strategy to prepare BP/polymer nanocomposites. Different from the traditional accurate controllable polymerization process through living radical polymerization, the BP/polymers are generally obtained by mixing BP with polymers and followed by a thermal or an UV curable process as shown in Figure  5. In addition, BP/polymer hydrogels are also inductive to PM.[69,90,120] For example, Yu’s group selected biocompatible and biodegradable PDLLA to load BP NSs.[60] The obtained BP/PDLLA hydrogel showed good temperature sensitivity and was demonstrated as a decent platform for postsurgical treatment of cancer. Zhang and coworkers fabricated a BP/polymer hydrogel by using agarose which is commonly considered as a harmless material for humans by the American Food and Drug Administration (FDA).[24c] Such a hydrogel represents a reversible hydrolysis and softening process, resulting in an accelerated release of anticancer drugs from the matrix to the surrounding under NIR light exposure. Wu et  al. first dispersed PPMS (PPMS-EPO) and BP NSs in DCM solution via ultrasound. The mixture was then dropped onto the surface of polished TiOH and a BP/PPMS (PPMS-EPO) film was fabricated by thermal curing in a vacuum oven.[66] The BP/PPMSEPO film exhibited an excellent antibacterial rate of $99.3\\%$ and $99.2\\%$ against Escherichia coli and Staphylococcus aureus after 10 min of irradiation, respectively. Apart from the above applications in biomedicine, BP/polymers, prepared by PM, are also widely employed in many other fields.[77,98] By using a one-pot polycondensation process of hexachlorocyclotriphosphazene and $^{4,4^{\\prime}}$ -diaminodiphenyl ether on the surface of BP NSs, a crosslinking PZN modified BP (BP-PZN) was prepared and further incorporated into an epoxy resin (EP) through thermal curing to prepare BP-PZN/EP nanocomposites for flame retardancy.[76] Gong et  al. choose melamine-formaldehyde (MF) to first modify the BP (BP-MF), then appropriate amounts of BP-MF and 4,4-diaminodiphenylmethane (DDM) were mixed in acetone and stirred for $10\\mathrm{min}$ . After that, EP was added into the mixture and kept stirring for another $30~\\mathrm{min}$ . Finally, the mixture was placed in a vacuum oven at $60~^{\\circ}\\mathrm{C}$ for $^{2\\mathrm{h}}$ to remove the acetone and cured at of 100 and $150~^{\\circ}\\mathrm{C}$ for 2h, respectively. The obtained nanocomposite (BP-MF/EP) showed a high char yield of $70.9\\%$ .[97]  \n\n![](images/2e083223e5824e9830e6db1a1e8116f3a2be2ef484db21053eefe05274028539.jpg)  \nFigure 5.  Preparation of BP/polymers via PM methods. a,b) Thermal polymerization. c,d) In situ polymerization. a,b,d) Reproduced with permission.[58,60,76] Copyright 2018–2019, Wiley-VCH. Reproduced with permission.[75] Copyright 2019, The Royal Society of Chemistry.  \n\nof wearable BP electronics.[25c] Bao and coworkers selected to prepare BP/PVA nanofibers through ST method, and found that BP/polymers possess fast carrier dynamics together with a modulation depth of $10.6\\%$ .[30] Zhang et  al. also demonstrated that BP/PMMA fibers show broadband nonlinear optical response ranging from 400 to $1930\\ \\mathrm{nm}$ , which paves the way for practical optoelectronic applications of BP.[40] Blaker’s group used PLAG to encapsulate BP to obtain BP/PLGA fibers, which was proved to be an ideal material to study the release rate of phosphate ions over an 8 week period.[57]",
        "category": " Materials and methods"
    },
    {
        "id": 6,
        "chunk": "# 2.4. Other Methods",
        "category": " Materials and methods"
    },
    {
        "id": 7,
        "chunk": "# 2.3. Spinning Technology  \n\nSpinning technology (ST) has been developed into a popular technology to prepare continuous nanofibers, which is another important way to prepare BP/polymer fibers. The core part of ST is the spinning fluid composed of BP and polymers passing through a spinneret nozzle, leading to the formation of a liquid jet, which may change into solid fibers rapidly after cooling or removing the solvents. The solution spinning is the most applied way to prepare BP/polymer fibers in order to maintain the microstructures and to obtain a well-dispersed solution of BP. In addition, the most used BP spinning fluids are those containing polymers with excellent fluidity, homogeneity, and large cohesion, so as to make sure the continuous spinning flow under the driving force. Chen et al. reported a flexible $\\mathsf{B P}/$ CNT/TPU supercapacitor with high energy density through a microfluidic ST, which may provide a way for fabrication  \n\nApart from the three mainly adopted methods, there are also many other effective strategies to fabricate BP/polymers. Zhang et  al. used the electrochemical deposition method to prepare BP/PPy films which can serve as promising flexible supercapacitors.[25b] Tang’s group obtained a BP/PVA nanocomposite through freeze drying, where the BP and PVA are connected with strong hydrogen bonding.[63] The nanocomposites showed a robust mechanical property and excellent controllable NIR-responsive drug delivery. BP/Pluronic F127 was also prepared via freeze drying and it was found that this compound can be used for synergistic photothermal-chemotherapy.",
        "category": " Materials and methods"
    },
    {
        "id": 8,
        "chunk": "# 3. Properties of Black Phosphorus/Polymers  \n\nSpecific nanocomposites are usually applied for specialized fields owing to their outstanding advantages of nanocomposites with specificity of properties. BP has been demonstrated to be a suitable nanomaterial to construct BP/polymers with various special properties, and the most conspicuous aspects are the improved optical absorption, superior mechanical strength, and robust environmental stability, which guarantee expansive applications of the BP/polymers.",
        "category": " Results and discussion"
    },
    {
        "id": 9,
        "chunk": "# 3.1. Optoelectronic Properties  \n\nThe optoelectronics properties of BP based nanocomposites can also be improved through functionalization with suitable polymers, enabling applications in fields such as tumor treatment, nonlinear optical properties, biomarker detection, electronic and optoelectronic devices.  \n\nFor example, the photothermal conversion efficiency is critical for nanomaterials to be used in PTT as photothermal agents. To enhance the photothermal conversion efficiency of BP NSs, PDA has been used to coat BP through a simple oxidative polymerization of dopamine in an alkaline environment. The photothermal conversion efficiency of the resulting $\\mathtt{B P}@\\operatorname{PDA}$ nanocapsules was increased due to the strong NIR absorbility of PDA. When irradiated with an $808~\\mathrm{nm}$ laser, enhanced heat generation was observed for these B $\\mathrm{\\cdotP}@\\mathrm{PDA}$ nanocapsules, so contributing to a better tumor PTT efficiency.[62]  \n\nThe changes in optical properties can also be used in detection of biomarkers. For instance, Zhou et  al. prepared a BP based fiber optic biosensor for detection of the cancer biomarker human neuron-specific enolase (NSE). Here, BP was coated on a fiber device with an in situ layer-by-layer method. Poly-L-lysine (PLL) was used for functionalization of the BP. Antibody recognizing NSE was then immobilized through PLL. Binding of the NSE by the antibody changed the local refractive index, enabling real-time detection of NSE with ultrahigh sensitivity.[121]  \n\nThe properties of electronic and optoelectronic devices can be further improved by functionalization with suitable polymers. For instance, the external quantum efficiency of $\\mathrm{Cs}\\mathrm{Pb}{\\mathrm{Br}}_{3}$ based perovskite light-emitting diodes (PeLEDs) can significantly increase from $0.7\\%$ to $2.8\\%$ by utilizing BP/polystyrene sulfonate as the hole injection layer in a PeLED stack.[122] Lee et  al. demonstrated a BP-based nonvolatile memory transistor by using PVDF-trifluoroethylene as the ferroelectric top gate insulator, which not only improved the stability of the transistors at ambient air, but also achieved high on/off ratios $_{(\\approx10^{5})}$ , high linear mobility values $(\\approx1159\\ \\mathrm{~cm^{2}~V^{-1}~s^{-1}})$ , and content memory properties with a 12 V window.[123]",
        "category": " Results and discussion"
    },
    {
        "id": 10,
        "chunk": "# 3.2. Mechanical Properties  \n\nThe excellent mechanical properties have proven essential for applications of BP based nanocomposites in many fields. Incorporation of BP into different polymer matrices can lead to the formation of BP/polymers with enhanced mechanical properties, which can sustain the applicability of BP/polymers.  \n\nFor instance, Huang et  al. prepared a BP based hydrogel scaffold to enhance bone regeneration. The hydrogel scaffold was obtained through photo-crosslinking of gelatin methacrylamide, BP, and cationic arginine-based unsaturated PEAs. SEM images of the hydrogel without BP showed a macroporous sponge-like structure with a mean pore size of about $50~{\\upmu\\mathrm{m}}$ . Incorporation of BP NSs led to the formation of a hydrogel with thicker walls. Correspondingly, the compression modulus of the hydrogel was also increased upon BP NSs incorporation. Releasing of phosphate from the hydrogel showed feeble influence on the mechanical properties of the BP/hydrogel. Meanwhile, biomineralization and bone regeneration was accelerated by this hydrogel.[86] Yang et al. reported NIR light controlled drug delivery and release with PVA based BP hydrogels. BP NSs were functionalized with PDA first and subsequently incorporated into the PVA hydrogel through a freezing/thawing method. Through formation of strong hydrogen bonding interaction within the hydrogel, the PDA modified BP NSs functioned as physical cross-linkers for PVA chains to enhance the mechanical properties of the hydrogel. Both tensile and compression tests confirmed the enhanced mechanical properties of the PVA hydrogel incorporated with PDA modified BP NSs. With enhanced mechanical properties and excellent reactivity to NIR light, this hydrogel turned out as promising in bioapplications, like artificial articular cartilage and drug delivery agents.[63] Ni et al. also studied the enhanced mechanical properties of BP/PVA nanocomposites. The formation of saturated P-O bonds outside the BP NSs enhanced their stability in air. Meanwhile, the mechanical properties (strength, toughness, and modulus) of the composite was dramatically increased by the interaction between BP NSs and PVA.[115]  \n\nZhang and coworkers fabricated a self-standing BP/PPy nanocomposite film through a facile one-step electrodeposition route.[25b] The prepared film showed good flexibility thanks to the friction between the BP and the polymer matrix, leading to increased toughness, mechanical strength, and modulus. The film can be bent with a large angle ranging from $0^{\\circ}$ to $180^{\\circ}$ , and such a prepared film can still retain almost $90\\%$ of its original capacitive value after 200 times bending. Chen’s group reported a BP/CNT/TPU nanocomposite film for a high energy density flexible supercapacitor.[25c] The prepared flexible film showed excellent mechanical strength with a Young’s modulus of $313~\\mathrm{MPa}$ and break elongation of $17.96\\%$ , respectively, which can be cut into different shapes and bended, rotated, twisted, and folded for many cycles. Bonaccorso et  al. found that the BP/PMMA nanocomposite shows about $106\\%$ improvement in Young’s modulus compared to the bare polymer.[124] Cheng’s group reported that the BP/PVA nanocomposite shows a maximum tensile strength of $316.9\\pm12.1\\mathrm{{\\:MPa}}$ , which is about 1.9 times higher than that of pure PVA films with the addition of 3.11 wt% BP.[115]",
        "category": " Results and discussion"
    },
    {
        "id": 11,
        "chunk": "# 3.3. Stability  \n\nThe relatively low stability in ambient conditions largely restricts the application of BP based nanomaterials. Oxygen and water have been considered to be the sources for the BP degradation. Detailed analysis of this process has shown that the reaction of oxygen with the surface of BP is the main cause of BP degradation.[125] The stability of BP NSs is also dramatically affected by light which can generate different kinds of reactive oxygen species (ROS) in the presence of oxygen and water. The reaction of ROS with the surface of BP results in the formation of $\\mathrm{P}_{x}\\mathrm{O}_{\\gamma}$ causing degradation of the BP NSs. It has been found that the ultraviolet part of the light spectrum is the main contributor to the degradation.[13d] Therefore, isolation of oxygen from BP has been the main strategy to enhance the stability of BP based nanomaterials by means of functionalization with suitable polymers. For example, PLGA is an FDA approved polymer with a degradation period spanning several months. The stability of BP QDs has been dramatically improved after incorporation into PLGA through the SC method. The size of the resulting BP QDs/PLGA nanospheres was about $100\\ \\mathrm{nm}$ . Through this strategy, the stability of BP QDs was effectively improved after incubation in phosphate-buffered saline (PBS) for 8 days, no dramatic loss of light absorbance and heat generation in response to $808~\\mathrm{nm}$ light irradiation was observed. After intravenous injection, the nanospheres were enriched in tumor tissues through an enhanced permeability and retention (EPR) effect. As a result, a more dramatic heat generation and tumor inhibition was achieved with these nanospheres after $808{\\mathrm{nm}}$ light irradiation.[126] PDA can also significantly improve the stability of BP based nanomaterials. As shown in ref. [62] after polymerization of dopamine, a layer of tight PDA could be coated on the surface of BP NSs. Both oxygen and water could be isolated from the internal BP NSs, resulting in enhanced stability. Both the size and the photothermal conversion of $\\mathtt{B P@}$ PDA could be maintained even after a long-term incubation at ambient conditions, enabling the utilization of these nanoconjugates in drug delivery and tumor treatment.[62]  \n\nThe instability of BP in physiological media also restricts its application in biomedical research. Because of the electron screening effect, pristine BP tends to aggregate and precipitate in media containing salts. Functionalization with polymers effectively improves the stability of BP based nanomaterials in physiological conditions. For example, Tao et al. utilized PEG- $\\cdot\\mathrm{NH}_{2}$ to coat BP NSs to enhance the stability in physiological media like PBS and cell culture media. $\\mathrm{PEG}\\mathrm{-NH}_{2}$ interacts with BP NSs mainly through electrostatics and when incubated in PBS or cell culture media, pristine BP NSs form aggregates with size up to about $1\\upmu\\mathrm{m}$ . This process was abolished by functionalization with PEG- $\\cdot\\mathrm{NH}_{2}$ , enabling a successful application of BP-PEG nanocomposites in tumor treatment.[44]  \n\nZhang et  al. reported that the modification of BP with PIL-TFSI can improve the environmental stability of BP.[23a] They found that the oxygen content in BP-based photodetectors (PDs) quickly increases from $5.5\\%$ to $49.1\\%$ while only about a $2.3\\%$ increase of oxygen content can be detected in a BP-PIL-TFSI-based PD after exposure in ambient air for 90 days. Additionally, Hu et al. also proved that the introduction of PIL can strongly enhance the environmental stability of BP. The BP-PIL-TFSI-based PD showed high flexibility, as well as great detectivity with almost no obvious deterioration in performance after $120\\mathrm{~h~}$ .[127] Cheng et  al. claimed that the PVA-coated BP nanocomposites present enhanced air-stability owing to the formation of outside saturated PO bonds.[115] Wen and coworkers applied PEDOT:PSS to coat BP; the obtained BP/PEDOT:PSS nanocomposite showed electrical conductivity as well as improved environmental stability in oxygen-rich water environments, which can offer a new opportunity for the practical applications of BP in electronics and optoelectronics.[128] Stable BP can also be obtained by sonication-assisted liquid-phase exfoliation (LPE) in the presence of MMA followed by radical polymerization.[129] Feng et  al. unveiled that PDDA can serve as hydrophilic ligands to improve the dispersity of BP in water and that BP/PDDA can maintain its properties even when exposed 15 days in both water and air.[51] Xu et  al. utilized an easy strategy to stabilize BP QDs by making a uniform BP/PMMA nanocomposite fiber film via the ST method, and found the same nonlinear optical properties for this compound as for fresh BP QDs.[40]",
        "category": " Results and discussion"
    },
    {
        "id": 12,
        "chunk": "# 4. Applications of Black Phosphorus/Polymers",
        "category": " Introduction"
    },
    {
        "id": 13,
        "chunk": "# 4.1. Optoelectronic Applications  \n\nAs described above, BP/polymers can strongly enhance the stability of BP. Besides that, BP/polymers can also improve the optical, mechanical, electrical and thermal properties of BP, which can strengthen the applications of BP in various areas. In this section, we summarize the applications of BP/polymers in optoelectronics. Especially in laser technology, ultra-stable pulses can be readily achieved from pulsed lasers based on $\\mathsf{B P}/$ polymers with great stability in environments. The advances of BP/polymers in other optoelectronic applications like PDs, random access memories and light-emitting diodes (LEDs) are here also covered.",
        "category": " Results and discussion"
    },
    {
        "id": 14,
        "chunk": "# 4.1.1. Laser Applications  \n\nUltrashort pulses with high energy have a variety applications such as nonlinear microscopy,[130] micromachining,[131] frequency combs,[132] and in biological research.[133] Saturable absorbers (SAs), which act as optical switches to convert continues waves into pulses, play a significant role for laser cavities.[134] In general, SAs can be divided into fast SAs and slow SAs according to response time. Fast SAs, like nonlinear polarization evolution (NPE) devices and nonlinear optical loop mirrors (NOLM), which possess a nearly instantaneous response time with deep modulation depth, are appropriate to generate ultrashort pulses with high energy.[135] However, NPEs are sensitive to environmental perturbations and do not support self-starting mode-locked operations; NOLMs usually require accuracy control over the power splitting, which affects its practical application. In contrast, a self-starting and stable mode-locked operation can be achieved with slow SAs. With the development of materials science, the response time of slow SAs can reach the femtosecond regime, which is suitable for ultrashort pulse generation. Semiconductor saturable absorber mirrors (SESAMs) are the most common slow SAs in the market, which can be attributed to their outstanding saturable absorption performance,[136] whereas the sophisticated fabrication and packaging mechanism of SESAMs increase the cost.[137] In addition, SESAM only have a few tens of nanometer operation bandwidth (narrowband operation) in the NIR,[136c] which seriously hinders the applications of SESAM in the field of midinfrared lasers. Recently, 2D materials have shown promising applications in electronics and photonics.[1e,3d,138] Their excellent nonlinear optical absorption makes them suitable as SAs in laser systems. Graphene was the first demonstrated 2D material SAs in laser systems (fiber based,[139] solid state,[140] waveguide[141]) due to fast recovery time,[142] broad operation bandwidth,[143] and low cost fabrication. However, the output performance of the laser is seriously hindered due to the low modulation depth of graphene $(2.3\\%$ for monolayer[144,145]). Subsequently, a series of 2D materials with different properties, like topological insulators (TI),[146] TMDs,[147] MXenes,[148] and BP materials, have been demonstrated as SAs in laser systems. BP has joined the 2D family with layer dependent direct bandgaps from 0.3 to $1.5\\mathrm{eV},^{[149]}$ and so bridges the bandgap between zero-gap graphene and large-gap TMDs $(1{-}2\\ \\mathrm{eV})$ for near and mid-infrared photonics and optoelectronics. Even though BP has lots of merits, an inevitable issue is the poor stability of BP in environments. As discussed in this review, incorporation with different polymers can effectively slow down the degradation rate and improve the environmental stability of BP,[150] which paves the way for ultrafast laser systems based on BPSA. Here, we summarize the recent progress for BP/polymers acting as SAs used in ultrafast laser systems (Table 2).  \n\nXu et al. proved that the stability of BP QDs can be improved by fabricating BP QDs/PMMA composite nanofiber films via an electrospinning technique. The application of the Z-scan method could prove that BP QDs/PMMA can maintain outstanding nonlinear optical properties for three months. A 1.07 ps pulse duration at the central wavelength of 1567.6 nm can be achieved from Er-doped mode-locked fiber lasers based on BP QDs/PMMA as a SA.[40] Feng et  al. selected PDDA to adsorb on the surface of few layers through electrostatic interaction. The results exhibited that the PDDA not only enhances the environmental stability of BP, but also improves the dispersity of BP in water. Moreover, it allows PDDA-BP to stabilize in both air and water more than 15 days of exposure, as shown in Figure  6. Hence, ultra-stable pulses with 1.2 ps pulse duration at $1557.8~\\mathrm{nm}$ can be obtained from Er-doped PML fiber lasers using PDDA-BP SA (Figure 7).  \n\nQ-switching is another technique to achieve pulses with high energy. Wu et al. reported a PVA-BP based $635\\mathrm{nm}$ Q-switching $\\mathrm{Pr}^{3+}$ doped fiber laser, the pulse duration was 383 ns and the tunable pulse repetition rate ranging from 108.8 to $409.8\\mathrm{kHz}$ .[38] Liu et  al. achieved 283.91 nJ pulse energy from a BP/PMMA based fiber laser, which is the largest pulse energy among Q-switched fiber lasers with BP SA at $1.5~{\\upmu\\mathrm{m}}$ .[53] Mu et  al. demonstrated two fabrication approaches to produce BP/PMMA films, the schematics of the two methods (sandwiched method and the ST) are shown in Figure  8a and b, respectively. A Q-switching operation can be obtained once the pump power reaches $25{\\mathrm{~mW}},$ which is a low threshold compared with those of graphene[151] and TMDs based SAs.[152] The output performance is shown in Figure  8c–f. The output spectrum bandwidth is $1.5\\ \\mathrm{nm}$ at the central wavelength of $1561.9\\ \\mathrm{nm}$ (Figure  8c) and the pulse train interval is $42.5~{\\upmu\\mathrm{s}}$ , which corresponds to a $23.48\\mathrm{kHz}$ repetition rate (Figure 8d). The output pulse duration is $4.35~\\upmu\\mathrm{s}$ and the radio frequency (RF) spectrum is around 53 dB shown in Figure 8e,f, respectively.",
        "category": " Results and discussion"
    },
    {
        "id": 15,
        "chunk": "# 4.1.2. Other Optoelectronic Applications  \n\nIn addition to its wide application in laser systems, BP/polymers have great application potential also in other fields, such as, field-effect transistors (FET),[22b,153] random access memories,[154] LED,[122] high-capacity lithium ion batteries, and PDs.[155] By applying poly PIL-TFSI into encapsulated BP QDs, Zhang et  al. demonstrated photoelectrochemical-type photodetector applications. The stability of BP can be significantly enhanced. In addition, the BP PDs possess self-healing capability and the typical ON/OFF signals can still be detected after 50 cycles attributing to the self-healing property of PIL-TFSIs, as shown in Figure 9. Ricciardulli et al. denoted that by introducing BP as a hole injection layer in LED stacks, the output and efficiency of perovskite based LEDs can be enhanced by increasing the hole injection and morphology of the $\\mathrm{Cs}\\mathrm{Pb}{\\mathrm{Br}}_{3}$ structure.[122] Li et al. demonstrated an original passivation method in that using poly (2-hydroxyethyl methacrylate)-co-poly (styrene) (PHMA-co-PS) it could improve the electrical transport properties for BP transistors at high electric fields.[153b] By applying the PHMA-co-PS encapsulation technique, the breakdown characteristics of BP FETs could be greatly improved and the on/off ratios increased by one order and four orders of magnitude in room and cryogenic temperatures, respectively. Meanwhile, this encapsulation technique showed outstanding stability in air as well as compatibility with mainstream semiconductor device manufacturing, promoting a potential application of wafer-scale. Figure  10 exhibits output characteristics of unencapsulated and encapsulated BP devices at different temperatures. Figure 10d shows that the maximum drain current can reach $1.2\\mathrm{mA}\\upmu\\mathrm{m}^{-1}$ at $20~\\mathrm{K}$ in BP FETs with PHMA-co-PS.  \n\nTable 2.  Performance summary of ultrafast lasers based on BP/ploymer as SA.   \n\n\n<html><body><table><tr><td>Material type</td><td>Layers</td><td>Technology</td><td>Laser type/wavelength</td><td>Repetition rate</td><td>Time</td><td>Energy</td><td>Ref</td></tr><tr><td>BP/PMMA</td><td>4-25 nm</td><td>Q-switching</td><td>Er/1561.9</td><td>7.86-34.32 kHz</td><td>4.35-2.96 μs</td><td>194 nj</td><td>[30]</td></tr><tr><td>BP/PC</td><td>15</td><td>Q-switching</td><td>Er/1550</td><td>35.7-70.6 kHz</td><td>6.2-1.65 μs</td><td>25.2 n)</td><td>[33]</td></tr><tr><td>BP/PVA</td><td>-</td><td>Mode-locking</td><td>Er/1533, 1558</td><td>20.8214 MHz 20.8221 MHz</td><td>700 fs</td><td>0.07 nj</td><td>[37]</td></tr><tr><td>BP/PVA</td><td>3</td><td>Q-switching</td><td>Pr3+/635</td><td>108.8-409.8 kHz</td><td>1560-383 ns</td><td>27.6 nj</td><td>[38] </td></tr><tr><td>BP/PDMS</td><td>9-24</td><td>Q-switching</td><td>Er/1064.7</td><td>26-76 kHz</td><td>5.5-2.0 μs</td><td>17.8 n)</td><td>[39] </td></tr><tr><td>BP/PMMA</td><td>1-3</td><td>Mode-locking</td><td>Er/1567.6</td><td>11.01 MHz</td><td>1.07 ps</td><td></td><td>[40] </td></tr><tr><td>BP/PVA</td><td>7</td><td>Mode-locking</td><td>Er/1562</td><td>5.268 MHz</td><td>1.438 ps</td><td></td><td>[49] </td></tr><tr><td>BP/PVA</td><td>70-100 nm</td><td>Q-switching</td><td>Er/1567.8-1565.3</td><td>64.51-82.64 kHz</td><td>3.39-1.36 μs</td><td>148.63 nj</td><td>[50] </td></tr><tr><td>BP/PDDA</td><td>3-7</td><td>Mode-locking</td><td>Er/1557.8</td><td>6.317 MHz</td><td>1.2 ps</td><td></td><td>[51] </td></tr><tr><td>BP/PDMS</td><td>-</td><td>Mode-locking</td><td>Er/1559</td><td>13.8MHz</td><td>650 fs</td><td>1.70 mW</td><td>[52] </td></tr><tr><td>BP/PMMA</td><td></td><td>Q-switching</td><td>Er/1561.21-1564.16</td><td>10.35-30.10 kHz</td><td>25.01-2.98 μs</td><td>283.91 nj</td><td>[53]</td></tr></table></body></html>  \n\n![](images/f389f012770df966709252a92f59bcede99b25cf070c3bbe68e0b020a5a5e267.jpg)  \nFigure 6.  Experiment on the stability of exfoliated PDDA-BP NSs. a) AFM images of bilayer PDDA-BP-1 nanosheets at the special region exposure under ambient conditions after 1, 7, 10, and 15 days (scale bar, $3\\upmu\\mathrm{m})$ . AFM: atomic force microscope. b,c) Raman spectra evolution and XPS spectra of the P element in bilayer PDDA-BP NSs against the exposure time in air. XPS: X-ray photoelectron spectroscopy. d) Intensity ratio of the $\\mathsf{A}_{\\mathrm{g}}^{\\mathrm{~l~}}/\\mathsf{A}_{\\mathrm{g}}^{\\mathrm{~\\tiny~\\dot{2}~}}$ from Raman spectra of PDDA-BP-1 exposure under ambient conditions after 15 days; e) Intensity ratio of the $\\mathsf{P O}_{x}/2\\mathsf{p}_{3/2}$ as a function of exposure time from XPS. a–e) Reproduced with permission.[51] Copyright 2018, American Chemical Society.  \n\n![](images/613c723c43af9b3bd702975bc007806b7758aecd622e7f3cd3712aa8db4fe0db.jpg)  \nFigure 7.  a) Experimental set up of an Er-doped PML fiber laser using a BP-PVA SA. LD: Laser diode, WDM: Wavelength division multiplexer, EDF: Erbium-doped fiber, OC: Output coupler, ISO: Polarization insensitive isolator, SMF: Single-mode fiber, PC: Polarization controller. b) Nonlinear transmission of BP at $1.5\\upmu\\mathrm{m}$ . c) Output spectrum. d) Intensity autocorrelation fitted by sech2. e) Output pulse train. f) Radio frequency (RF) spectrum. Inset: Wideband RF spectrum of $600~\\mathsf{M H z}$ . a–f) Reproduced with permission.[51] Copyright 2018, American Chemical Society.  \n\n![](images/8349b5941ae187b12a7f5b71070929125849f0aef6dce6b6e82e178fe3916029.jpg)  \nFigure 8.  a) Fabrication process of sandwiched PMMA-BP-PMMA membranes. b) Diagrams exhibiting the fabrication of BP-PVP nanocomposite membranes by the electrospinning technique. c) Output spectrum. d) Output pulse train. e) Intensity autocorrelation. f) RF spectrum. Inset: Wideband RF spectrum of $780~\\mathsf{k H z}$ . a–f) Reproduced with permission.[30] Copyright 2015, Wiley-VCH.",
        "category": " Results and discussion"
    },
    {
        "id": 16,
        "chunk": "# 4.2. Bio-Applications  \n\nThe applicability of BP in biomedical fields has been widely investigated. With excellent photoelectronic properties, BP has been shown to be a promising candidate for bio-imaging and phototherapies, such as PTT and PDT.[156] The large surface area of BP NSs enables highly efficient drug loading and delivery. Meanwhile, the degradation of BP results in in situ formation of phosphate, which is an important raw material for bone regeneration. BP has also been applied for antibacterial treatment, for gene editing, and for neurodegenerative diseases, etc.[157] Functionalization of BP with suitable polymers has turned out critical for the successful application of BP in the biomedical field. The biocompatibility and stability of BP can be efficiently improved when coated with polymers such as PEG and PLGA. Meanwhile, polymer functionalization of BP provides moieties for further modification of the nanocomposites with targeting ligands and other functional groups, which are important for optimization of therapy efficiency and reduction of side effects.[62] Moreover, the incorporation of BP into certain polymers enables fabrication of various hydrogels and scaffolds with unique characteristics, suitable for applications in tissue engineering.[24c]  \n\n![](images/731a1a7b0f3eab40d4adb41e1ec8f4126e63869066487bf293914ce0c5cc4d75.jpg)  \nFigure 9.  Photo-response behavior of BP-PIL-based PDs. a) Linear sweep voltammetry (LSV) curve of BP-PIL. b) Photo-response behavior of the PD at $-0.6\\:\\vee$ in different concentration KOH solution. c) Photo-response behavior with different potential in $0.75~\\mathsf{m}$ KOH solution. d) Long-term stability test of BP-PIL-based PD. e) Photo-response behavior of the as-prepared PDs after different cycles of self-healing. f) $P_{\\mathsf{p h}}$ as the function of different self-healing cycles. a–f) Reproduced with permission.[23a] Copyright 2019, Wiley-VCH.  \n\n![](images/7bd565a7b7e27b868bddfc0b482f466bd848ef25a3a370aacdca6db5800c3a8b.jpg)  \nFigure 10.  a,b) Output properties of unencapsulated and encapsulated BP FETs with PHMA-co-PS at $300~\\mathsf{K}$ ( $\\boldsymbol{\\mathrm{V_{d}}}$ is from 0 to $-4\\lor$ ). c,d) Breakdown characteristics of the unencapsulated and encapsulated BP devices at $20~\\mathsf{K}$ $(V_{\\mathrm{g}}$ is from 2 to $-6\\mathsf{V}$ in steps of −1 V). a–d) Reproduced with permission.[153b] Copyright 2019, Wiley-VCH.",
        "category": " Results and discussion"
    },
    {
        "id": 17,
        "chunk": "# 4.2.1. Bio-Imaging  \n\nBio-imaging refers to the visualization of biological structures and processes through noninvasive strategies. With layer dependent fluorescence, high photothermal conversion efficiency and excellent loading capacity, BP based nanomaterials have attracted much interest in fluorescence imaging, photothermal imaging, and photoacoustic (PA) imaging.[156]  \n\nBecause of quantum size effects, layer dependent fluorescence has been detected with few layer BP based nanomaterials, suitable for fluorescent imaging of cells and tumors.[158] Meng et  al. measured by means of an LPE method the photoluminescence lifetime of BP nanoparticles with lateral size and thickness of 35 and $6\\mathrm{nm}$ , respectively. Photoluminescence emission at $690~\\mathrm{nm}$ was observed, the lifetime of which was shown to be 110.5 ps.[159] BP QDs fabricated with a pulsed laser ablation method also showed stable blue–violet photoluminescence emission with a quantum yield as high as $20.7\\%$ .[160] Because of the large surface area of BP, BP/polymers are also suitable for loading and delivery of fluorescent agents for bioimaging. Li et  al. reported the application of PEGylated BP QDs for loading of the fluorescent RdB molecule (Figure 11a). Functionalization with PEG improved the physiological stability and biocompatibility of the BP QDs (Figure  11c). Loading of RdB enabled efficient imaging of tumor cells (Figure  11d).[45] Deng et al. modified small BP nanoparticles with dextran and poly(ethyleneimine), which enabled further functionalization with folic acid (FA) and cyanine 7 (Cy7). The resultant BP nanoparticles showed excellent stability, biocompatibility and tumor targeting ability. Both PA imaging and NIR fluorescence imaging of tumors were realized with these nanoparticles, suitable for imaging guided diagnosis and treatment of tumor.[67]  \n\nWith excellent photothermal conversion efficiency, BP based nanomaterials are also ideal agents for photothermal imaging. When intravenously injected, they accumulate in tumor tissues through the EPR effect. Following NIR light irradiation, heat is generated in the tumor tissues and can be easily detected with a thermal imaging camera. Combinations with polymers enhance the physiological stability, tumor targeting efficiency or photothermal conversion efficiency of the BP based nanomaterials. For example, functionalization of BP NSs with PEG enhances the stability in physiological media. When an FA moiety is attached through PEG, enhanced retention of the nanocomposites in cervical cancer models has been observed, making it possible to improve the tumor specificity of photothermal imaging.[44] To enhance the photothermal conversion efficiency of BP NSs, Zeng et al. modified them with PDA. The stability of BP NSs in ambient environment was so dramatically enhanced through isolation of both oxygen and water by the PDA modification. Meanwhile, the tumor targeting efficiency of the nanocomposites could be enhanced through further modification of PDA through Michael addition or Schiff base reactions. With light adsorption of PDA, the photothermal conversion efficiency of the nanocomposites was also improved. All these processes contributed to better photothermal imaging and PTT mediated inhibition of breast cancer.[62]  \n\nPA imaging uses contrast agents to absorb energy from short laser pulses to generate thermo-elastic expansion, which is detected by ultrasonic transducers to show tissue structures with high temporal and spatial resolution, deep tissue penetrability and excellent sensitivity.[161] Contrast agents are critical for PA imaging. Because of their intense and stable signals, various nanomaterials, including BP/polymers, have been shown to be excellent contrast agents for PA imaging.[162] For instance, Sun et al. reported the application of PEGylated BP nanoparticles in PA imaging of tumors. High yield production of water-soluble and biocompatible BP/PEG conjugates was prepared with a one-pot solventless high energy mechanical milling method. High photothermal conversion efficiency and excellent photostability under NIR light irradiation was so observed with these nanoconjugates. Upon administration through intravenous injection, the nanoparticles accumulated in tumors through the EPR effect, enabling detection of tumors with PA imaging.[24b]  \n\n![](images/2c1e2fc77767b219b3244c2924ce53bbc65c0c58d1e56fb7f6ba7476ec5906f5.jpg)  \nFigure 11.  Loading of RdB with PEGylated BP QDs for cell imaging. a) Schematic illustration of the functionalization and RdB loading of BP QDs for imaging and tumor inhibition. b) TEM image of RdB/PEG-BP QDs. c) Biocompatibility of PEG-BP QDs detected with HepG2 cells. d) Fluorescence imaging of HepG2 and 4T1 cells with RdB/PEG-BP QDs. a–d) Reproduced with permission.[45] Copyright 2017, American Chemical Society.  \n\nTable 3.  Examples of BP/polymers applied in PTT of cancer.   \n\n\n<html><body><table><tr><td>Material type</td><td>Size/height [nm] </td><td>Laser</td><td>Model</td><td>Remarks</td><td>Ref.</td></tr><tr><td>BP/PEG</td><td>3.2 ± 1.0, 1.2 ± 0.6</td><td>808 nm, 2 W cm-2, 5 min</td><td>4T1 breast cancer</td><td>PA imaging guided PTT</td><td>[24b] </td></tr><tr><td>BP/PEG</td><td>2.6,1.5</td><td>808 nm, 1 W cm-2, 10 min</td><td>C6 glioma cells and MCF7 breast cancer cells</td><td>Excellent photothermal conversion efficiency and photostability</td><td>[31] </td></tr><tr><td>BP/PLGA</td><td>102.8 ± 35.7</td><td>808 nm, 1 W cm-2, 10 min</td><td>MCF7 breast cancer</td><td>Excellent stability and biodegradability</td><td>[126] </td></tr><tr><td>BP/PEG-FA/DOX</td><td>120,1-2</td><td>808 nm, 1.0 W cm-2, 10 min</td><td>HeLa cervical cancer</td><td>Tumor specific drug delivery and PTT</td><td>[44]</td></tr><tr><td>BP/PDLLA/PEG/PDLLA</td><td>/</td><td>808 nm, 0.5 W cm-2, 5 min</td><td>HeLa cervical cancer</td><td>Sprayable and biodegradable hydrogel for PTT and postsurgical treatment of cancer</td><td>[60] </td></tr><tr><td>BP/PDA/PEG-Apt</td><td>200-300,12.6</td><td>808 nm, 1.0 W cm-2, 10 min</td><td>MCF7 breast cancer</td><td>Enhanced stability and photothermal performance, relief of multidrug-resistance</td><td>[62]</td></tr><tr><td>BP-DEX/PEI-FA/Cy7</td><td>15-40, 1.6-4.3</td><td>808 nm, 1.5 W cm-2, 2 min</td><td>4T1 breast cancer</td><td>NIR Fluorescence imaging and PA imaging guided PTT</td><td>[67]</td></tr><tr><td>BP/cellulose hydrogel</td><td>一</td><td>808 nm, 1 W cm-2, 5 min</td><td>Huh7 hepatocellular carcinoma</td><td>Injectable hydrogel for PTT</td><td>[69]</td></tr><tr><td>BP/Pluronic F-127</td><td>一</td><td>808 nm, 2.0 W cm-2, 5 min</td><td>4Tl breast cancer</td><td>Thermo-sensitive hydrogel for drug delivery and PTT</td><td>[78]</td></tr><tr><td>BP/PLLA/PEG/PLLA</td><td>164.1 ± 14.8</td><td>808 nm, 1.0 W cm-2, 10 min</td><td>T47D breast cancer</td><td>Sensitization of tumor through downregulation of heat</td><td>[104]</td></tr><tr><td>BP/PLGA</td><td>165.5±55</td><td>808 nm, 1.0 W cm-2, 5 min</td><td>U251 glioma</td><td>shock protein 90 Mesenchymal stem cells mediated tumor targeting</td><td>[105]</td></tr></table></body></html>\n\nFA: Folic acid, DOX: Doxorubicin, DEX: Dextrin, Apt: Aptamer.",
        "category": " Results and discussion"
    },
    {
        "id": 18,
        "chunk": "# 4.2.2. Tumor Treatment  \n\nBP/polymers have also been widely investigated for tumor treatment. Upon administration, these nanoparticles can accumulate in tumor tissue through the EPR effect. With excellent NIR light response, BP/polymers can be activated in deeper tissues, enabling non-invasive tumor treatment. When irradiated with light of suitable wavelength, either hyperthermia or ROS can be produced by BP, enabling PTT or PDT mediated tumor inhibition.[44,163] Benefitting from the extremely high surface areas of BP, BP/polymers are also idea carriers for loading and delivery of various cargos (drugs, nucleic acids, proteins, etc.) for combined tumor treatment.[164]  \n\nEspecially, conjugation of BP/polymers with various tumor targeting ligands (FA, Transferrin, polysaccharides, peptides, antibodies, and aptamers recognizing tumor specific surface makers) has enabled efficient tumor specific delivery of these nanomaterials and cargos. This widely applied strategy has largely enhanced the efficiency, tumor specificity and biocompatibility of the therapy.  \n\nPhotothermal Therapy: Traditional tumor therapies like radiotherapy, chemotherapy and surgery, face challenges of side effects, and tumor recurrence. In searching for new tumor therapies, nanomaterial-mediated PTT has drawn much attention recently. In PTT, nanomaterials with high photothermal conversion efficiency have been delivered into tumor tissues followed by irradiation with light of suitable wavelength for heating generation in situ that can kill tumor cells. Because of its non-invasiveness, high efficiency, and specificity, PTT has been extensively investigated in treatments of various tumors and several groups of nanomaterials with excellent photothermal conversion efficiency have been developed for usage in PTT of tumors.  \n\nBP/polymers are also prominent photothermal agents for PTT of tumors. Various polymers have been utilized in surface modification of BP NSs and BP QDs for PTT of several kinds of tumors. Incorporation of BP with suitable polymers has also enabled the preparation of hydrogels for intratumoral injection and postsurgical treatment (Table 3). In 2015, Sun et al. proved the potential of BP QDs as photothermal agents for tumor treatment. $28.4\\%$ photothermal conversion efficiency was observed with NIR light exposure of BP QDs, indicating their excellent photothermal performance. The photostability of BP QDs was also high. After functionalization of the BP QDs with PEG, the stability in physiological media was increased, enabling their usage in cell culture. BP/PEG nanocomposites showed excellent biocompatibility in several types of cells. Stimulation with NIR light led to efficient induction of cancer cell death through PTT.[31] Sun et al. furthermore investigated a high yield preparation of PEGylated BP nanoparticles with an one-pot solventless high energy mechanical milling technique. The BP/PEG nanocomposites obtained with this strategy were water-soluble and biocompatible. When exposed to NIR light, excellent photothermal conversion was observed, enabling complete ablation of tumors in vivo through PTT.[24b]  \n\nShao et al. loaded BP QDs into PLGA to prepare biodegradable BP QDs/PLGA nanospheres with an emulsion method (Figure  12a,b). This strategy protected the BP QDs from external water and oxygen and increased the photothermal stability of BP QDs (Figure  12c,d). The rate of degradation of the BP QDs was also controlled by the hydrophobic PLGA (Figure  12e). These nanospheres were highly biocompatible (Figure  12f). When injected intravenously, an excellent tumor targeting ability was observed (Figure 12g,h). Benefitting from the excellent photothermal conversion efficiency and stability of these nanospheres, heat generation in the tumor tissues was detected when irradiated with NIR light (Figure 12i). Excellent tumor inhibition efficiency was achieved, further revealing the potential of BP/polymers for PTT of tumors (Figure 12j).[126]  \n\nXing et  al. reported the preparation of injectable composite hydrogels with BP NSs and cellulose for PTT of tumors. The hydrogels were biocompatible and showed excellent photothermal conversion efficiency and flexibility, suitable for tumor ablation with PTT.[69]  \n\nBP/polymers are also used in PTT mediated postsurgical treatment of tumors. Through incorporation of BP NSs with a thermosensitive hydrogel [poly(oplactide)-poly(ethylene glycol)- poly(bplactide) (PDLLA-PEG-PDLLA: PLEL)], a $\\mathtt{B P}\\ @$ PLEL hydrogel was prepared with excellent biodegradability, biocompatibility, photothermal conversion efficiency, and possibility for NIR light-induced sol–gel transition. When sprayed and irradiated with NIR light, the hydrogel formed a gelled membrane on tumor surgery caused wounds. The residual tumor tissues were ablated by PTT. Meanwhile, bacteria were also killed by hyperthermia to prevent infection.[60]  \n\n![](images/6e0cd50b98e7c8bbcffa1cb5ef096e774471eadff9002f0f6f2340674c9ff8e5.jpg)  \nFigure 12.  BP QDs/PLGA nanospheres for PTT of tumor. a) TEM images of BP QDs. b) SEM images of BP QDs/PLGA nanospheres. c) Photothermal performance of BP QDs after storage in water for indicated times. d) Photothermal performance of BP QDs/PLGA nanopheres after storage in water for indicated times. e) SEM images of BP QDs/PLGA nanospheres after storage in PBS for indicated times. f) Viability of cells after incubation with BP QDs/PLGA nanospheres for $48\\mathrm{~h~}$ . g) Tumor retention of BP QDs/PLGA nanospheres after intravenous injection. h) Quantitative analysis of BP $\\mathsf{Q D s}/$ PLGA nanospheres in tumor and main organs. i) Changes of tumor temperature following intravenous injection and laser irradiation. j) Changes of tumor size after indicated treatments. a–j) Reproduced with permission.[126] Copyright 2016, Springer Nature.  \n\nTable 4.  Representative BP/polymers applied in PDT of cancer.   \n\n\n<html><body><table><tr><td>Material type</td><td>Size/height [nm] </td><td>Laser</td><td>Model</td><td>Remarks</td><td>Ref.</td></tr><tr><td>BP/PEG/PAA</td><td>197</td><td>808 nm, 1.44 W cm-2, 10 min </td><td>U14 cervical cancer</td><td>UCNP enabled highly efficient PDT with 808 nm laser</td><td>[36]</td></tr><tr><td>BP/PEG</td><td>2.5± 0.7, 1.3 ± 0.7</td><td>625 nm, 80 mW cm-2, 10 min </td><td>4T1 breast cancer</td><td>Fluorescence imaging guided PDT/PTT</td><td>[45] </td></tr><tr><td>BP/PEI/AuNPs</td><td>491.7 ± 4.9</td><td>670 nm,</td><td>HepG2 hepatocellular</td><td>Localized surface plasmon resonance enhanced PDT</td><td>[68]</td></tr><tr><td>BP/RhB-MnO-FITC</td><td>120,59.3</td><td>1 W cm-2, 5 min 660 nm,</td><td>carcinoma HeLa cervical cancer</td><td>Oxygen self-supply, microenvironment responsive</td><td>[89] </td></tr><tr><td>Apt-BMSF@Pt</td><td>52.3 ± 5.7</td><td>0.15 W cm-2,10 min 670 nm,</td><td>HepG2 hepatocellular</td><td>and bio-imaging guided PDT Hepatocellular carcinoma-specific, oxygen</td><td>[91] </td></tr><tr><td>BP/PDA-Ce6&TPP</td><td>213.9</td><td>0.1 W cm-2, 5 min 660 nm, 1 W cm-2, 10 min</td><td>carcinoma HeLa cervical cancer</td><td>self-compensate Mitochondria-targeting PTT/PDT</td><td>[92]</td></tr></table></body></html>\n\nUCNP: Upconversion nanoparticles, RhB: Rhodamine B, Ce6: Chlorin e6, TPP: Triphenyl phosphonium, BMSF: BPQD-hybridized mesoporous silica framework, FITC: Fluorescein isothiocyanate.  \n\nPhotodynamic Therapy: PDT is seen as a promising noninvasive tumor treatment strategy and has been widely investigated in recent years. During PDT, photosensitizers (PSs) are introduced into tumor tissues, followed by light exposure to stimulate production of ROS in the tissues. ROS produced in tumor cells leads to peroxidation of lipids, proteins and DNA, resulting in apoptosis, necrosis, or autophagy-mediated tumor cell death. Microvascular systems in tumor tissues can be damaged by ROS, leading to shortage of oxygen and nutrients in the tumor tissues. Interestingly, ROS mediated damages to tumor tissues in PDT also stimulate complex reactions to host immune systems, leading to long-term tumor inhibition.  \n\nAs a critical component of PDT, PSs can have dramatic impact on the therapeutic efficiency. Several generations of PSs have been developed for PDT. However, several drawbacks of traditional PSs, such as low photo-stability, high hydrophobicity, and lack of tumor specificity, have largely restricted the clinical applications of PDT. The recent introduction of nanomaterials in PDT have turned the situation around and have promoted the development of therapy.[165] Nanomaterials are ideal carriers for a traditional PS to enhance the photo-stability and tumor targeting efficiency. Several kinds of nanomaterials, such as, BP, can also catalyze the production of ROS in response to light stimulation, which renders them to be utilized as PSs in PDT.[165] When conjugated with different polymers, BP based nanocomposites with various functions are fabricated for PDT of cancer. Further modification of the polymers may enhance the targeting efficiency, ROS production and tumor inhibition efficiency of PDT (Table 4).  \n\nIn 2015, Wang et  al. reported the application of BP NSs as PS in PDT. Upon $660\\ \\mathrm{nm}$ laser exposure, singlet oxygen was generated with a quantum yield of about 0.91. In vitro and in vivo studies confirmed the therapeutic efficiency of BP NSs in PDT.[166] Chen et al. further confirmed the potential of BP NSs for applications in cancer treatments including PDT.[163] Guo et al. also reported the application of BP QDs in PDT.[167]  \n\nIn most cases of PDT applications, functionalization of BP with suitable polymers is required to increase the biocompatibility and reduce the side effects of the pristine BP. Li et al. reported the functionalization of BP QDs for combined PTT/PDT of cancer. The biocompatibility and physiological stability of BP QDs were improved after PEGylation, resulting in better combined therapeutic efficiency.[45] To further increase the singlet oxygen yields of BP NSs, Zhang et  al. integrated gold nanoparticles (AuNPs) with BP NSs with PEI as linker. The singlet oxygen generation of BP NSs in response to $670\\mathrm{nm}$ laser stimulation was dramatically enhanced by excitations of localized surface plasmon resonances, leading to more efficient suppression of tumor growth.[68] To increase the penetration depth of BP based PDT, Lv et al. combined upconversion nanoparticles with BP sheets. The BP sheets were functionalized with $\\mathrm{PEG}{\\cdot}\\mathrm{NH}_{2}$ to enhance the stability. Poly(acrylic acid) was used to modify upconversion nanoparticles. Then these two components were integrated through electrostatic interaction. The resulting nanocomposites catalyzed ROS production was obtained with high efficiency when irradiated with $808~\\mathrm{nm}$ NIR light, and showed excellent PDT effect both in vitro and in vivo.[36]  \n\nThe sensitivity of various organelles to ROS is quite different. Targeted delivery of PSs to organelles such as mitochondria has been proved to induce cancer cell death with higher efficiency. As the powerhouses of the cells, the normal structure and function of mitochondria is critical for cell survival. Meanwhile, mitochondria are also critical in regulation of apoptosis. ROS mediated damage of mitochondria has resulted in both shortage of energy and release of cytochrome C into cytosol, which triggered apoptosis of cancer cells. Yang et  al. reported the targeted delivery of BP nanosheet-based PS to mitochondria for PDT (Figure  13a). BP NSs were functionalized with PDA (Figure  13b), which enabled further ligation of the nanocomposite with both chlorin e6 (Ce6) and triphenyl phosphonium (TPP) through covalent bonds (Figure  13c). The resulting nanocomposite could generate both heat and ROS when exposed to a $660~\\mathrm{nm}$ laser, enabling synergistic PTT/PDT of tumor (Figure 13d,e). Upon administration, mitochondria-targeting was achieved with TPP (Figure 13f), resulting in ROS mediated damage of mitochondria following NIR light stimulation. Dramatically enhanced inhibition of cancer cell viability was realized with this nanocomposite (Figure 13g) and fluorescence imaging of tumors in vivo could then also be achieved (Figure  13h). A quite dramatic tumor inhibition was thus observed with this nanocomposite (Figure 13i).[92]  \n\n![](images/8a73e2a71a41ba4f1b5f3965d7f8b2d4ab89492752aaa2f4659d9d4369ada0ca.jpg)  \nFigure 13.  BP@PDA-Ce6&TPP nanosheets for mitochondria-targeting PTT/PDT of cancer. a) Schematics for the preparation and application of the nanocomposites. b) TEM image of $B P@\\mathsf{P D A}$ nanosheets. c) UV–vis–NIR spectra of the indicated nanosheets. d) Heat generation of ${\\mathsf{B P@P D A}}.$ Ce6&TPP nanosheets irradiated by $660\\ \\mathsf{n m}$ laser for 10 min. e) ROS generation of the indicated materials irradiated by $660\\ \\mathsf{n m}$ laser measured by absorbance decay of ABDA at $380~\\mathsf{n m}$ . f) Confocal fluorescence images of cells pre-treated with the indicated nanosheets and Mito-Tracker Green. g) Viability of HeLa cells exposed to a $660\\ \\mathsf{n m}$ laser for 5 min after incubation with the indicated nanomaterials. h) Fluorescence imaging of mice with tumor after injection of $\\mathsf{B P@}$ PDA-Ce6&TPP nanosheets. i) Tumor inhibition efficiency of $\\mathsf{B P@}$ PDA-Ce6&TPP nanosheets. a–i) Reproduced with permission.[92] Copyright 2019, The Royal Society of Chemistry.  \n\nConsidering the immune activation ability of PDT, it has been used to treat cancer in combination with immunotherapy. This combined strategy has been shown to be promising in inhibition of tumor metastasis and recurrence. BP nanoflakes coated by neutrophil membranes have been applied in activation of the immune system through PDT/PTT to inhibit lung metastasis of tumors.[168] Recently, Zhang et  al. prepared a BP/polymer based nano-regulator for activation of anti-tumor immune responses. PEGylated hyaluronic acid was coated on the surface of BP to enhance the stability, biocompatibility and targeting efficiency of the nanocomposite. Following the combined PDT/PTT with this nanocomposite, the tumor associated macrophage phenotype was altered from pro-tumor to anti-tumor. Through induction of immunogenic cell death and release of damage-associated molecular patterns, robust anti-tumor immune responses were evoked to inhibit both the original tumor and the metastatic tumor.[114]  \n\nDrug Delivery: As one of the most widely utilized tumor therapies, chemotherapy is both simple and cheap. However, systematically administered chemical drugs cause severe side effects to normal tissues, especially tissues with active cell division. Meanwhile, dramatic changes of drug concentration in the body largely promote the occurrence of side effects and reduces the tumor inhibition efficiency. Here tumor specific delivery and controlled release of chemical drugs can promote the therapeutic efficiency and safety of chemotherapy. Nanomaterials are ideal carriers for this purpose. With the large surface area and excellent NIR light responsiveness, BP based nanomaterials are recognized as promising agents for targeted delivery and light controlled release of chemotherapy drugs. When functionalized with different polymers, the physiological stability, tumor specificity, and therapeutic efficiency of BP based nanomaterials can be effectively improved.  \n\nTao et al. reported the delivery and controlled release of the chemotherapy drug doxorubicin (DOX) with PEGylated BP NSs (Figure 14a). BP NSs were first functionalized with PEG to enhance the stability and biocompatibility. When an FA moiety was attached through PEG, the tumor targeting efficiency of the nanocomposites was increased (Figure 14b,e,f). A DOX loading capacity up to $108\\%$ was observed, which is dramatically higher than for many other nanoparticle-based drug delivery systems (Figure 14c,d). In an acidic environment, the DOX release from PEGylated BP NSs was accelerated, making it possible for a tumor microenvironment promoted drug release. When irradiated with $808~\\mathrm{nm}$ NIR light, the DOX release was further increased, showing the potential to control drug release with NIR light. In in vitro systems, the viability of cancer cells was dramatically inhibited by this combined strategy. Meanwhile, the tumor inhibition efficiency was effectively improved with this strategy in tumor models (Figure $\\mathrm{14g)}$ .[44]  \n\nBP based hydrogels are also used for drug delivery. Qiu et al. reported the application of low-melting point agarose based BP hydrogels for tumor specific delivery and NIR light controlled release of DOX. When irradiated with $808~\\mathrm{nm}$ NIR light, the hydrogel softened and melted because of the generation of heat by BP NSs, leading to release of DOX specifically in tumor tissues. Importantly, the rate of DOX release could be precisely controlled through modulation of the NIR light and hydrogel composition. Meanwhile, this BP hydrogel was highly biocompatible and degradable. Efficient inhibition of both breast cancer and melanoma was achieved with this BP hydrogel.[24c] Yang et  al. prepared a composite hydrogel with PDA modified BP NSs (pBP) and PVA through a freezing/thawing approach. The hydrogel was biocompatible and showed excellent mechanical properties. Because of the photothermal conversion of pBP, ondemand drug release was achieved with this hydrogel through NIR light stimulation.[63]",
        "category": " Results and discussion"
    },
    {
        "id": 19,
        "chunk": "# 4.2.3. Bone Regeneration  \n\nDamage to bones is widely occurring in injuries and diseases such as tumors and osteitis. Currently, autografts, allografts and artificial bone scaffolds, are much used in the clinic for the treatment of bone injuries. However, autografts of bones often result in damage to normal bones. Furthermore, allografts of bones are limited by the risk of immunological rejection and disease transmission. It is often more convenient and safer to use artificial bone scaffolds for the repair of bone injuries. However, it is still challenging to fabricate artificial bone scaffolds with excellent biocompatibility, osteoinduction, and osteointegration with traditional materials. The recent development of nanomaterials provides new opportunities for the design of better bone substitutes for repair of bone injuries.[169]  \n\nBP/polymers are also excellent candidates for design of artificial bone substitutes for the repair of bone injuries and regeneration of bones.[169] Compared with nanomaterials such as graphene, BP/polymers are superior in that the degradation of BP results in the formation of phosphate anions in situ to provide raw materials for the regeneration and mineralization of bones. Besides, the excellent photothermal conversion efficiency, the ROS production ability and the drug loading capability of BP make it possible for modulation of bone regeneration processes through diverse strategies. Furthermore, modification of BP with different polymers can enhance the biocompatibility, stability, and bone targeting efficiency, all contributing to better therapy effects.[169]  \n\nAs a critical constituent of bone, phosphorus is required for bone regeneration. A variety of materials containing phosphorus have been shown to promote the mineralization and regeneration of bones. Interestingly, the degradation of BP results in in situ production of $\\mathrm{PO}_{4}{}^{3-}$ , which participates in bio-mineralization through capturing of $\\mathrm{Ca}^{2+}$ . Increased abundance of phosphate ions in bone-forming cells treated with BP NSs promotes the formation of mineral clusters on endoplasmic reticulum (ER) membrane. The mineral clusters are transported from ER to mitochondria before they are further transported to extracellular matrices for the initiation of biomineralization.[171] Taking advantage of this unique character, Huang et  al. reported the preparation of a BP nanosheetbased hydrogel scaffold for bone regeneration through photocrosslinking of gelatin methacrylamide, BP NSs and cationic arginine-based unsaturated poly(ester amide)s. The embedding of BP NSs improved the mechanical properties of the hydrogel and enabled a photo-induced phosphate release. The osteogenic differentiation of dental pulp stem cells was improved by this hydrogel, and enhanced bone regeneration was also observed in vivo with this hydrogel.[86]  \n\nBesides, the highly efficient photothermal conversion of BP may also contribute to bone regeneration as mild heat stimulation already has been shown to stimulate such regeneration. Based on such phenomenon, Tong et  al. designed an osteoimplant with PLGA coated BP NSs. When stimulated with low intensity and periodic NIR light, the mild photothermal conversion of the implant stimulated the expression of heat shock proteins in tissues, leading to enhanced osteogenesis.[172] Wang et  al. also reported the application of PLGA coated BP QDs in bone regeneration (Figure  15a). To enhance the targeting efficiency, a cell-specific aptamer was utilized for the functionalization of the nanocomposites to prepare bioinspired matrix vesicles (Figure  15b,e). The stability of BP QDs was enhanced after PLGA functionalization (Figure  15c,d). The local concentration of inorganic phosphate was increased by this targeted delivery strategy, resulting in enhanced bio-mineralization. Meanwhile, light stimulation of the matrix vesicles increased the temperature and stimulated the expression of alkaline phosphatase and heat shock proteins, both of which contributed to bone regeneration (Figure  15f–h). In vivo experiments confirmed the highly efficient bone targeting ability of the bioinspired matrix vesicles (Figure  15i). As a result, the bone regeneration in vivo after injury was dramatically improved with this strategy (Figure 15j).[170] Pan et al. reported the treatment of rheumatoid arthritis with a plateletrich plasma-chitosan thermoresponsive hydrogel incorporated with BP NSs. The hyperplastic synovial tissue in inflamed joints was removed by heat and ROS generated from BP NSs in response to NIR light stimulation. The phosphate released from BP NSs thus provided materials for osteanagenesis. Meanwhile, the friction between tissues was reduced by the hydrogel. All of these processes contributed to the observed therapy outcomes of the hydrogel.[106]  \n\n![](images/eefc7525a9d3cd375418b1110157482881d4511d98c20b9b51f591cd565238ef.jpg)  \nFigure 14.  BP-PEG nanocomposite for tumor specific delivery and NIR light controlled release of DOX. a) Schematics for the functionalization of BP NSs with PEG and DOX loading on the BP-PEG nanocomposite. b) STEM image and EDS mapping of BP-PEG-FA nanosheets. c) UV–vis–NIR spectra of BP-PEG/DOX nanosheets at indicated drug feeding ratios. d) Drug loading capacity of a BP-PEG nanocomposite at indicated drug feeding ratios. e) NIR imaging of tumor bearing mice injected with BP-PEG/Cy7 (G1) or BP-PEG-FA/Cy7 (G2). f) Distribution of BP-PEG/Cy7 (G1) or BP-PEG-FA/Cy7 (G2) in main organs and tumors of the injected mice. g) Tumor inhibition efficiency of the indicated treatments. a–g) Reproduced with permission.[44] Copyright 2017, Wiley-VCH.  \n\n![](images/4ce62180849f663ada58785f8da7b6cf46769387354328b1b2d028f7fd8e4a2a.jpg)  \nFigure 15.  Bioinspired BP-PLGA matrix vesicles (MVs) for bone regeneration. a) Overview of the application of the MVs for bone regeneration. b) Preparation of the MVs. c) SEM image of the MVs. d) Photothermal conversion of the MVs after storage in PBS for indicated times. e) Osteoblast targeting ability of the MVs. f) Alizarin Red staining of cells after indicated treatments. g) ALP expression after indicated treatments. h) Runx2 expression after indicated treatments. i) Bone targeting efficiency of the MVs. j) Bone regeneration after indicated treatments. a–j) Reproduced with permission.[170] Copyright 2019, Springer Nature.  \n\nMaking use of the excellent drug loading capability of BP NSs, BP/polymers have also been successfully applied in delivery of drugs for bone regeneration. Wang et  al. reported an NIR light triggered delivery of $\\mathrm{SrCl}_{2}$ with BP based microspheres for bone regeneration. PLGA was coated onto the surface of the nanocomposites to enhance the stability and biocompatibility. When irradiated with NIR light, the flawing of the PLGA shells resulted in a controlled release of ${\\mathrm{Sr}}^{2+}$ , enabling precise control of drug release locally at optimal time periods. As an element with characteristics similar to calcium, strontium enhances bone regeneration through induction of osteoblast differentiation and inhibition of osteoclast activation.  \n\nExcellent bone regeneration capacity was achieved in a rat femoral defect model.[64]  \n\nExtracellular matrices are also critical for bone regeneration and BP/polymers can be used for modulation of extracellular matrices to promote bone regeneration. For example, Wang et  al. reported the construction of nanoengineered hydrogels through the incorporation of BP NSs into double network hydrogels to mimic the extracellular matrix microenvironment for induction of bone regeneration. The formation of CaP crystal particles was induced by BP NSs. An extracellular matrix microenvironment suitable for the differentiation of osteogenic cells and regeneration of bones was formed with this hydrogel.[90]  \n\nBP/polymers are also promising materials for fabrication of scaffolds for bone regeneration. Yang et al. reported the preparation of 3D printed scaffolds reinforced by BP for combined therapy of osteosarcoma enabled by the photothermal effects of the BP NSs. Meanwhile, the bio-mineralization driven by phosphorus promoted the regeneration of bone in situ.[173] Lee et  al. reported the fabrication of BP-incorporated poly(e-caprolactone) and collagen (PCL/BP/Col) nanofiber matrices as bone tissue engineering scaffolds. With excellent biocompatibility, the nanofiber matrices promote the implant, cell division, and osteodifferentiation of preosteoblasts.[85] Liu et al. reported the preparation of 3D printed scaffolds composed of BP and graphene oxide (GO) nanosheets for bone regeneration. Positively charged poly(propylene fumarate) was used as scaffolds for the adsorption of BP/GO composites. The surface area of the scaffolds was thereby increased, which is suitable for the attachment of cells. The differentiation of osteoblasts was stimulated by phosphate released from the degraded BP NSs. Both bio-mineralization and osteogenesis was enhanced with these 3D scaffolds.[174]",
        "category": " Results and discussion"
    },
    {
        "id": 20,
        "chunk": "# 4.2.4. Gene Knockdown  \n\nModulation of gene expression levels, especially down-regulation of gene expression, is important for studies of gene functions and treatment of diseases. One of the most widely used tools for knockdown of gene expression is to use small interfering RNA (siRNA). Traditionally, siRNA is introduced into cells with transfection reagents such as lipofectamine. However, lack of targeting ability and the potential for side effects restrict the clinical application of this strategy. Recently, several kinds of newly discovered nanomaterials have been successfully used in loading, targeted delivery and controlled release of siRNA for gene knockdown. BP/polymers are also promising for this purpose. Zeng et al. prepared BP NSs-based nanocapsules with PDA modification for siRNA delivery and gene knockdown (Figure 16a). To enhance the tumor targeting efficiency, an AS1411 aptamer was attached to the nanocapsule through chemical reactions with PDA. Both DOX and siRNA targeting P-gp were successfully loaded into this nanocapsule. The release of DOX could be regulated by both acid and NIR light (Figure  16e). Meanwhile, efficient delivery of the siRNA in tumor cells resulted in downregulation of the P-gp protein expression (Figure 16f). The tumor resistance to DOX through P-gp was thus relieved (Figure  16g), contributing to the good breast cancer inhibition effect of nanocapsules (Figure 16h).[62] Wang et  al. designed BP based nanocomposites for silencing of Survivin expression. BP NSs were coated with polyethyleneimine for delivery of siRNA targeting Survivin. Knocking down of Survivin expression with these nanocomposites suppressed the growth of tumors and enhanced the tumor inhibition efficiency of PTT.[175]  \n\nBesides, clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 and related systems are also widely applied in down-regulation of gene expression. In these systems, both Cas9 proteins and guiding RNA are delivered into cells for gene editing or mRNA splicing. Nanomaterials including BP/polymers have also been investigated as carriers for delivery of these components to modulate gene expression. For example, Zhou et  al. reported effective gene-editing with the CRISPR/Cas9 system loaded on BP nanosheets. To enhance the loading and nuclear targeting efficiency, three nuclear localization signals were engineered to the C-terminal of Cas9 protein. The nanocomposites were taken up by cells through membrane penetration and endocytosis pathways. The biodegradation of BP resulted in endosomal escape and cytosolic release of the Cas9 complexes, leading to highly efficient gene-editing.[176] Recently, Yue et al. prepared PLL-functionalized BP nanosheets for delivery of the CRISPR/Cas13a system into tumor cells. A crRNA was codelivered to knock down the expression of Mcl-1. After endocytosis and endosomal escape, a knocking down efficiency of $58.64\\%$ was achieved with this nanocomposite, enabling the application of this strategy in tumor treatment.[108]  \n\n![](images/31c3526613ddcb9d4d91f87c8fd843c16203e90dd01da0c645af394721fdfd0e.jpg)  \nFigure 16.  Knocking down of P-gp protein with a PDA-modified BP nanocapsule for tumor treatment. a) Schematics for the preparation of the nanocapsule for siRNA delivery and tumor treatment. b) TEM images of the nanocapsule. c) AFM images of the nanocapsule. d) Height profiles along the lines in (c). e) Release of drug from the nanocapsule in acid environment with or without NIR light stimulation. f) Knocking down of P-gp with the nanocapsule. g) Release of drug in MCF/ADR cells. h) Tumor inhibition efficiency of the nanocapsule irradiated with NIR light. a–h) Reproduced with permission.[62] Copyright 2018, Wiley-VCH.",
        "category": " Results and discussion"
    },
    {
        "id": 21,
        "chunk": "# 4.2.5. Biosensors  \n\nBiosensors are devices used to detect the existence and concentration of certain substances in biological systems. With the ability to detect various biomarkers with high sensitivity, biosensors have become important tools for diagnosis of human diseases such as cancer and neurodegenerative disease. Like many other nanomaterials, BP/polymers have been widely investigated for applications in biosensing of biological components and disease markers.  \n\nThe excellent photoelectric properties and biocompatibility of BP ensure the sensitive detection of various biological components, while the functionalization with different polymers enhances the stability of BP. For instance, Kumar et  al. proved the encapsulation of BP NSs with polypeptide micelles for fabrication of biosensors. BP NSs were exfoliated with sonication in a polar solvent. They were subsequently encapsulated with micelles prepared with PEG and poly(phenyl isocyanidepeptide) based copolymer blocks. The stability and biocompatibility of BP NSs were improved by this strategy. Meanwhile, the electronic properties of BP NSs were not affected, enabling integration in devices for biosensing.[72]  \n\nBiosensors based on BP/polymers have been successfully applied in detection of various substances. For example, Zhao et  al. prepared a biosensor composed of PLL and BP nanoflakes. A water-phase exfoliation protocol was developed for the preparation of BP nanoflakes (Figure  17a,b). The PLL was subsequently coated on the nanoflakes via hydrophobic and electrostatic interaction. Finally, hemoglobin (Hb) was attached to this PLL-BP hybrid. The protein conformation and function of the Hb was maintained. Direct electron transfer between Hb and electrode was detected and a good reduction activity toward $\\mathrm{O}_{2}$ and $\\mathrm{H}_{2}\\mathrm{O}_{2}$ was so observed with this biosensor (Figure 17c,d). A linear dependence between the electrochemical response and $\\mathrm{H}_{2}\\mathrm{O}_{2}$ concentration was also revealed (Figure  17e).[47] Zhen et  al. reported the preparation of a biosensor with a nanocomposite consisting of an ionic liquid, poly(diallyldimethylammonium chloride) and BP. Hb was then immobilized onto this nanocomposite. Electrocatalytic activity toward nitrite reduction was detected with high sensitivity and stability.[73] Zhang et al. also reported the fabrication of a vitamin C biosensor made of BP QDs, polypyrrole and poly(3,4-ethylenedioxythiophene) nanorods. A linear relationship between the peak currents and vitamin C concentration ranging from 0.01 to $4\\mathrm{mm}$ was observed. The detection limit was shown to be $0.0033\\mathrm{~mm}$ . Successful detection of vitamin C was achieved with this biosensor with excellent reproducibility, stability, and selectivity.[48]  \n\n![](images/56f3e2c33261a31384e65cff80712032b0946c7568adecd722ec463417d46673.jpg)  \nFigure 17.  Preparation of a $H\\mathsf{b}@$ pLL-BP biosensor. a) TEM images of BP nanoflakes collected at different centrifugation speeds (Left, 3000 rpm. Right, $5000~\\mathsf{r p m})$ . b) Raman spectra of BP nanoflakes and bulk BP. c) Cyclic voltammogram of $H b@$ pLL-BP glassy carbon electrode (GCE) saturated with $\\mathsf{N}_{2}$ air or $\\mathsf{O}_{2}$ . d) Cyclic voltammogram of Hb@pLL-BP GCE saturated with ${\\sf N}_{2}$ with or without ${\\sf H}_{2}{\\sf O}_{2}$ . e) Cyclic voltammogram of Hb@pLL-BP GCE in PBS with ${\\sf H}_{2}{\\sf O}_{2}$ of different concentration. a–e) Reproduced with permission.[47] Copyright 2018, American Chemical Society.  \n\nBP/polymers based biosensors have also been investigated for detection of proteins. For example, Liu et  al. reported the detection of lysozyme with a BP QDs-based biosensor. This biosensor was based on anodic electrogenerated chemiluminescence generated from a reaction of BP QDs and $\\mathrm{{Ru(bpy)}}_{3}{}^{2+}$ . Styrene-acrylamide copolymer nanospheres were used for encapsulation of BP QDs to enhance its stability and provide functional amino groups for connection with DNA. The nanospheres were then immobilized onto an electrode coated with lysozyme aptamers through the DNA. The specific interaction between lysozyme and the aptamer led to release of the nanospheres and decrease of the electrogenerated chemiluminescence signal. This enabled the detection of lysozyme with high sensitivity and selectivity.[71]",
        "category": " Results and discussion"
    },
    {
        "id": 22,
        "chunk": "# 4.3. Energy Storage Devices  \n\nIn recent decades, energy storage devices have developed rapidly, such as Li-ion batteries and supercapacitors, due to the available portable electronics and the gradually growing demands of electrical energy storage/supplying components with high-performance.[3f,177] In this respect, BP possesses splendid properties like light molecular weight, large interlayer spacing $(5.3\\mathring\\mathrm{\\A})$ , high theoretical capacity $(2596\\ \\mathrm{mA}\\mathrm{h}\\ \\mathrm{g}^{-1})$ , and good electrical conductivity $(\\approx300\\mathrm{~S~m^{-1}})$ , something that has made BP become a reliable electrode material for energy storage devices.[178] Recent advances have thus witnessed the applications of BP/polymers in alkali-ion batteries, supercapacitors, and nanogenerators.[12c,179]",
        "category": " Results and discussion"
    },
    {
        "id": 23,
        "chunk": "# 4.3.1. Ions-Batteries  \n\nIon batteries, like ${\\mathrm{Li^{+}}}$ and $\\mathrm{{Na^{+}}}$ batteries, have been considered as clean and efficient candidates for fabricating energy storage devices in large-scale.[180] BP has attracted lots of interest thanks to its high theoretical capacity and low working potential. Additionally, theoretical investigations have revealed that the large interlayer spacing of BP endows a fast intercalation and diffusion of metal ions.[181] Zarbin et al. fabricated PANI coated BP cathodes for aqueous Na-ion batteries, which exhibit a specific capacity of $200~\\mathrm{{mA}}$ h $\\boldsymbol{\\mathrm{g}}^{-1}$ after 50 cycles in NaCl solution under ambient conditions.[93] Wan’s group reported a ternary nanocomposite consisting of BP, graphite, and PANI (BP-G/PANI) for working as anodes of Na-ion batteries (Figure 18a).[70] They demonstrated that the nanocomposites can effectively reduce the charge transfer resistance, and can supply an optimized ion pathway from electrolyte to PANI to BP-G and finally to BP. Besides, the PANI can also prevent BP from volume expansion, which can ensure a stable cycling performance of the battery. The as-prepared battery shows a high reversible gravimetric capacity of $1530~\\mathrm{mA}$ h $\\mathrm{g}^{-1}$ and a capacity retention of $520\\ \\mathrm{mA}\\ \\mathrm{h}^{-1}$ after 1000 cycles as shown in Figure 18b,c. Subsequently, Duan and et al. demonstrated that BP can be applied as the active anode for high-rate, high-capacity, Li storage with robust cycle performance.[110] They reported that graphitic carbon can generate covalent bonds with restrained edge reconstruction within the layered BP particles, which can prevent the reconstruction of edges and ensure a fast entry of the ${\\mathrm{Li^{+}}}$ ions. Li et  al. prepared a PVA gel-polymer coated BP electrolyte for a three-electrode flexible zinc–nickel battery.[46] In the BP/PVA electrolyte, PVA served as the matrix while BP served as the barrier for $\\mathrm{Zn(OH)_{4}}^{2+}$ . The battery exhibited the typical flexibility (Figure  18d–f) and an initial discharge capacity of $509.8\\mathrm{\\mA}\\mathrm{\\h\\g}^{-1}$ , which can retain at $212.8\\mathrm{\\mAh}$ $\\mathbf{g}^{-1}$ after 100 cycles.",
        "category": " Results and discussion"
    },
    {
        "id": 24,
        "chunk": "# 4.3.2. Supercapacitors  \n\nAs reliable fast charging energy storage devices to narrow the gap between capacitor and battery and owing to their great potential as a physical charge storage at the electrolyte/electrode interface, supercapacitors have been conceived to provide a stable power output after almost infinite numbers of cycles at a large current density.[183] BP/polymers have been applied for supercapacitors with exciting results due to their large surface area and the stacking layers for efficient intercalation of ions, see Table  5 which shows the comparison of the performance of BP/polymers based rechargeable supercapacitors.[182,184] Figure  19a shows the preparation of a hybrid nanocomposite electrode composed of BP NSs and PANI $\\mathrm{\\langleBP/}$ PANI) by Pumera and coworkers. [25d] The BP/PANI electrode shows a specific capacitance of $354\\ensuremath{\\mathrm{~F~}}\\ensuremath{\\mathrm{g}}^{-1}$ as the current density of $0.3\\mathrm{~A~g^{-1}}$ . Zhang’s group developed a flexible laminated self-standing PPy/BP film through the one-step method of electrochemical deposition.[25b] The flexible film exhibited a low internal resistance with excellent charging/discharging cycles, with about $60\\%$ and $92\\%$ reserved capacitance under a high current density $(10\\mathrm{~A~g^{-1}})$ and different bending angles, respectively (Figure  19b–d). Chen et  al. assembled BP and CNT into non-woven fiber fabrics for a flexible supercapacitor through a microfluidic-spinning technique.[25c] The flexible supercapacitor possessed enhanced conduction, remarkable mechanical stability, and plentiful ion channels (pores $<1\\mathrm{nm}$ ). Figure 19e demonstrates the preparation and potential applications of a CNTs/BP-CNT nanocomposite supercapacitor. Benefiting from the above merits, the supercapacitor showed a large volumetric capacitance $(308.7\\mathrm{~F~}\\mathrm{cm}^{-3}.\\$ ), a high energy density $(96.5\\mathrm{~mW~h~}\\mathrm{cm}^{-3})$ ), and enhanced long cycle stability during deformation, indicating a great potential for the design of nextgeneration wearable electronics.  \n\n![](images/47b2d5ff776511b9bb97e459b4bd64d5abcbf24b15d995169a36c1e3b15a2043.jpg)  \nFigure 18.  a) Schematic illustration of BP-G and BP-G/PANI electrodes. b) Rate performance of BP-G/PANI electrode. c) Cycling stability of BP-G/PAN electrode. d–f) Digital photographs of flexible zinc-nickel battery. a–c) Reproduced with permission.[70] Copyright 2019, American Chemical Society. (d–f) Reproduced with permission.[46] Copyright 2018, Elsevier.",
        "category": " Results and discussion"
    },
    {
        "id": 25,
        "chunk": "# 4.4. Flame Retardancy  \n\nFlame retardancy technology has been established to satisfy the demands of social security development in fire protection, production and life, and protection of people’s lives and property.[185] Flame retardants are a kind of special chemical additives applied to enhance the combustion performance of combustible and flammable materials and which are generally applied for the flame retardancy processing of various decoration materials.[186] The materials that contain flame retardants can effectively delay, prevent or even terminate the spread of flames as they come into contact with external fire sources, so as to achieve the effect of flame retardancy. Similarly to graphene, and as one of the most adopted additives in polymer nanocomposites, few-layer BP has been considered as a novel nanofiller for manufacturing flame retardants owing to its outstanding features like mechanical property, thermal stability, and characteristic dimension effects.[77,96–98]  \n\nBP/graphene composites were distributed in waterborne PUA $(\\mathrm{BP/G}@\\mathrm{WPUA})$ by Luo et al.[59] The cone calorimeter tests reveal that BP/G/WPU exhibits a lower peak heat release rate (PHRR) of $235.4\\mathrm{kW}\\mathrm{m}^{-2}$ and total heat release of 51.68 MJ $\\mathrm{m}^{-2}$ , respectively. Tan et al. reported a melamine-formaldehyde (MP) functionalized BP $(\\mathrm{BP}@\\mathrm{MF})$ with the adsorption energy of $-0.63\\ \\mathrm{eV},$ indicating a strong mutual adsorption between MF and BP.[97] The further epoxy resin (EP) incorporated ${\\mathrm{BP}}\\ @{\\mathrm{MF}}$ shows a residual char of $19.4\\%$ at $400~^{\\circ}\\mathrm{C}$ . Hu et  al. fabricated $\\mathrm{-NH}_{2}$ group abundant PZN functionalized BP NSs (BP/PZN) through polymerizing hexachlorocyclotriphosphazene and $^{4,4^{\\prime}}$ -diaminodiphenyl ether on BP NSs.[76] EP was further used to coat BP/PZN for investigating its flame retardancy properties. As shown in Figure 20a, BP plays a special role to promote the formation of char as it captures most of the free radicals. The unique layered structure of BP can act as a special physical barrier, which can effectively insulate both oxygen and heat during the combustion process. Calorimeter test results show that there are about $859.5~\\mathrm{kW~m}^{-2}$ and 60.8 MJ $\\mathrm{m}^{-2}$ in PHRR and THR in $2\\mathrm{wt\\%}$ BP/PZN@EP at around $450^{\\circ}\\mathrm{C}$ , respectively. Figure 20b shows photos of the external residues of pure EP and $\\mathrm{BP/PZN}@\\mathrm{EP}$ from top and side views. There are few residual chars that can be seen in the pure EP while the residual chars show a gradually increasing trend in both amount and size with the increased contents of BP. Table  6 lists the summary of the performance of BP as an additive for flame retardancy. It is found that a certain amount doping of BP has great potential for fabricating nanocomposites with high-performance.  \n\nTable 5.  The performance of BP/polymers based rechargeable supercapacitors.   \n\n\n<html><body><table><tr><td>Materials</td><td>Type</td><td>Potential</td><td>Capacitance</td><td>Capacity retention</td><td>Ref</td></tr><tr><td>BP/PPy</td><td></td><td>-0.2-0.8V</td><td>515 F g-1 (1 A g-1)</td><td>48% (1000 cycles)</td><td>[182]</td></tr><tr><td>BP/PPy</td><td>Flexible</td><td>-0.1-0.7 V</td><td>497.5 F g l (0.5 A g-l)</td><td>65% (10 000 cycles)</td><td>[25b]</td></tr><tr><td>BP/PANI</td><td></td><td>-0.4-0.6 V</td><td>354 F g-l (0.3 A g-l)</td><td>-</td><td>[25d] </td></tr><tr><td>BP/CNTs/TPU</td><td>Flexible</td><td>0-3V</td><td>308.7 F cm-3 (0.1 A cm-3)</td><td>97.4% (1000 cycles)</td><td>[25c]</td></tr></table></body></html>  \n\n![](images/ee70fdd287b2b74ddbc60f915f9ab1b012d48f46c2c9152f041f4d5855091310.jpg)  \nFigure 19.  a) Schematic of fabrication of BP/PANI nanocomposite electrode. b) Cyclic voltammetry (CV) curves and c) galvanostatic charging/discharging (GCD) curves of PPy/BP film. d) Flexible performance of PPy/BP film under different bending angles. e) Illustration of a flexible CNTs/BP-CNTs nanocomposite supercapacitor via the hot-pressing method and the potential for electronic applications. Reproduced with permission.[25b,25d] Copyright 2018, American Chemical Society. Reproduced with permission.[25c] Copyright 2018, Springer Nature.",
        "category": " Results and discussion"
    },
    {
        "id": 26,
        "chunk": "# 4.5. Information Storage  \n\nThe accelerating development of the electronic information industry has promoted a lot of new technologies, including artificial intelligence, virtual reality, quantum information technology and so on, which has given rise to the fourth industrial revolution and a hastening of the end of the third. Thus, information storage has been considered as an essential area of social development. Resistive random access memories (RRAM), a newly emerged non-volatile technology with the advantages of simple structure and excellent data storage capacity has been widely explored for new-generation data storage applications in recent decades.[187]  \n\n![](images/ef1797e31dadaa3bf19211c468118d705b4ad9609b111b0615c2822ce9c6f522.jpg)  \nFigure 20.  a) Mechanism illustration of BP/PZN@EP composites. b) Digital photos of residue chars of pure EP and BP/PZN@EP from top and sid views. Reproduced with permission.[76] Copyright 2019, Wiley-VCH.  \n\nBP has been recognized as a promising material for fabricating information storage devices owing to its small switching bias window and high ON/OFF ratio which can effectively decrease the information misreading rate and unnecessary power consumption of memory devices. Peng et al. systematically investigated the memory characteristics of BP QD based resistive RRAMs through ex- and in situ control methods as shown in Figure 21a.[41] A large ON/OFF ratio of $3.0\\times10^{7}$ was found for the as-prepared memory device. Figure  21b shows a photograph and an illustration of BP/PVP-based memory devices by Zhang et  al.[32] The electronic and switching characteristics (Figure  21c) reveal the full electrically bistable behavior of the BP/PVP-based device. The high-resistance state (HRS) (OFF state) and low-resistance state (LRS, that is, ON state) represent the writing process as for typical digital memory devices. The device shows a high ON/OFF ratio of $6.0\\times10^{4}$ together with excellent stability for both the HRS and LRS, which demonstrated that the BP/PVP nanocomposite can serve as an electrically bistable material for flash memory devices. Chen et  al. reported an in situ synthesis of PDDF covalently functionalized BP for fabricating an RRAM device (Au/PDDF-g-BP/ITO).[58] The device exhibits a rewritable memory performance with a high ON/OFF ratio of $10^{4}$ and voltages of $+1.95$ and $-2.34\\mathrm{~V~}$ for turn on and off, respectively (Figure  21d–f). They further applied PFCz as the synthetic precursor to react with BP, and the as-prepared Al/PFCz-g-BP QDs/ITO device showed a large ON/OFF ratio of $10^{7}$ as well as low turn-on/off voltages of $-0.89/+1.95\\mathrm{~V}.$ Table  7 shows a comparison of memory performances of BP/polymers-based devices, suggesting that BP/polymers are promising candidates for RRAM devices.  \n\nTable 6.  Performance summary of flame retardants doped with BP.   \n\n\n<html><body><table><tr><td>Materials</td><td>BP content [wt%]</td><td>TPHRR[S]</td><td>PHRR</td><td>THR</td><td>Residual char [wt%]</td><td>Ref</td></tr><tr><td>BP/G@WPU</td><td>2.0</td><td>-</td><td>235.4 kW m-2</td><td>51.7 MJ m-2</td><td>12.5</td><td>[59] </td></tr><tr><td>BP/PZN@EP</td><td>2.0</td><td>149</td><td>859.5 kW m-2</td><td>60.8 MJ m-2</td><td>-</td><td>[76]</td></tr><tr><td>BP/EC@PUA</td><td>3.0</td><td>-</td><td>355.4Wg-l</td><td>34.9 k) gl</td><td>一</td><td>[77]</td></tr><tr><td>BP/TA@TPU</td><td>2.0</td><td></td><td>562.0 kW m-2</td><td>45.5 MJ m-2</td><td>9.7</td><td>[95] </td></tr><tr><td>BP/IL@TPU</td><td>1.5</td><td>一</td><td>700.0 W m-2</td><td>70.4 Mj m-2</td><td>6.3</td><td>[96] </td></tr><tr><td>BP/MF@EP</td><td>1.2</td><td>315</td><td>623.7 W g-l</td><td>34.6 k) g-l</td><td>19.4</td><td>[97]</td></tr><tr><td>BP/MCNTs@EP</td><td></td><td>120</td><td>988.6 kW m-2</td><td>63.5 MJ m-2</td><td>-</td><td>[98] </td></tr><tr><td>BP/(CFSO3)Er@EP</td><td>3.0</td><td>一</td><td>1450.0 kW m-2</td><td>65.7 MJ m-2</td><td>-</td><td>[99] </td></tr><tr><td>BP/graphene@ EP</td><td>2.0</td><td>-</td><td>1461.9 kW m-2</td><td>105.6 Mj m-2</td><td>48.0</td><td>[100] </td></tr><tr><td>BP/PVA@PDA</td><td>5.0</td><td></td><td>216.1 W g-l</td><td>34.2 k) g </td><td>5.4</td><td>[101] </td></tr><tr><td>BP/PEI@PUA</td><td>2.0</td><td></td><td>1158.0 kW m-2</td><td>71.0 MJ m-2</td><td>-</td><td>[102] </td></tr><tr><td>BP/COF@EP</td><td>2.0</td><td></td><td>796.7 kW m-2</td><td>74.9 MJ m-2</td><td>_</td><td>[103] </td></tr><tr><td>BP/TPU</td><td>2.0</td><td></td><td>507.0 kW m-2</td><td>52.0 MJ m-2</td><td>-</td><td>[111] </td></tr><tr><td>BP/graphene@TPU</td><td>0.9</td><td>二</td><td>1048.0 kW m-2</td><td>117.0 M) m-2</td><td>8.9</td><td>[112]</td></tr></table></body></html>\n\n$T_{\\mathsf{P H R R}}.$ : Time to PHRR.  \n\n![](images/be64a4c3b247c29f2cfb4ecad46abfd143d26aee44ea12b3be7cf384e8a53296.jpg)  \nFigure 21.  a) The preparation process of flexible BP/PMMA-based RRAMs. b) Illustration of BP/PVP-based memory device. c) The $1-V$ characteristics of a BP/PVP-based memory device. d) Effects of continuous read pulses on ON/OFF states current of the devices of $\\mathsf{I}.0\\mathsf{V}$ (pulse width $=70~\\mathrm{ms}$ , pulse period $=20~\\mathrm{ms}^{\\prime}$ ). e) $1-V$ curves of the devices. f) I–V curves of the device kept in ambient for over 90 days. a–f) Reproduced with permission.[32,41,58] Copyright 2019, Wiley-VCH.",
        "category": " Results and discussion"
    },
    {
        "id": 27,
        "chunk": "# 4.6. Other Applications  \n\nApart from the above applications, BP/polymers have also been widely applied in other fields due to their excellent properties. Li and coworkers developed a washable skin touch-actuated textile-based triboelectric nanogenerator consisting of BP and hydrophobic cellulose oleoyl ester nanoparticles on a PET fabric as shown in Figure 22a.[188] Such a prepared device reveals excellent reliability together with high triboelectricity under extreme conditions like hard washing, severe deformation, and longterm exposure under ambient conditions. Zeng et al. obtained a BP NSs/PI for ceramic-based dielectrics, which showed good interfacial compatibility, a high-permittivity value of 8.6 at $100\\mathrm{Hz}$ , and a low dielectric loss value of 0.02.[94] Lin et al. found that the appropriate addition of BP NSs in PEDOT:PSS could significantly increase the electrical conductivity (Figure 22b).[34] Soon afterward, Jeon et  al. demonstrated that the doping of BP NSs, with $2\\mathrm{\\wt\\%}$ addition, in PEDOT:PSS exhibits a power factor of $36.2\\upmu\\mathrm{W}\\mathrm{m}^{-1}\\mathrm{K}^{-2}$ , which is about $109\\%$ higher than for the pure PEDOT:PSS film (Figure 22c,d).[56] BP NSs were incorporated with PLGA fibers through a solution blow spinning method, which exhibits tunable release rates of phosphate ions and presents a great potential for bone tissue engineering.[57] Qaiss et  al. claimed that the addition of BP NSs into PVDF could dramatically decrease the thermal stability, and shown that the electrical conductivity could be sharply increased from $3.3\\times10^{-14}$ to $5\\times10^{-11}\\mathrm{S}\\mathrm{cm}^{-1}.^{[74]}$ Luo and coworkers found that the coefficient of friction decreased from 0.117 to 0.046 due to the constantly supplied BP NSs into the contact area with phosphorus oxide and phosphoric acid on the counterpart surface (Figure 22e,f ).[55,189]  \n\nTable 7.  The memory performance comparisons of BP/polymers-based RRAM devices.   \n\n\n<html><body><table><tr><td>Materials</td><td>Memory effect</td><td>Cycles</td><td>ON/OFF ratio</td><td>Switch-on voltage/V</td><td>Stability/s</td><td>Ref.</td></tr><tr><td>BP/PVP</td><td>Rewritable</td><td></td><td>4.0 × 104</td><td>-1.20</td><td>10</td><td>[32]</td></tr><tr><td>BP/PMMA</td><td></td><td>100</td><td>3.0×106</td><td>-2.80</td><td>104</td><td>[4]</td></tr><tr><td>BP/g-PDDF</td><td></td><td>200</td><td>1.0 × 104</td><td>+1.95</td><td>104</td><td>[58] </td></tr><tr><td>BP/g-PFCz</td><td></td><td>600</td><td>1.3 ×10</td><td>-0.89</td><td>104</td><td>[75]</td></tr></table></body></html>  \n\n![](images/59b5e1e69d231272b588ba11c00884a07f81d7e203f1feeeffffeb95e0259ffc.jpg)  \nFigure 22.  a) The fabrication process of a textile BP/polymer nanogenerator. b) Thermoelectric parameters of BP/PEDOT: PSS file. c,d) Release dynamics of BP/PLGA nanocomposite. e) Coefficient of friction as a function of time for BP/PEFE. f) Dielectric loss of BP/PI nanocomposite. a) Reproduced with permission.[188] Copyright 2018, Springer Nature. b–d) Reproduced with permission.[56,57] Copyright 2018, American Chemical Society. e) Reproduced with permission.[55,74] Copyright 2018–2019, Elsevier.",
        "category": " Results and discussion"
    },
    {
        "id": 28,
        "chunk": "# 5. Conclusion  \n\nSince the first appearance of few-layer black phosphorous (BP) in transistors in 2014, a large amount of attention has been attracted to explore its properties and applications. The special advantages of BP, like tunable band gap, high ON/ OFF ratio, and anisotropy in optical and thermal properties have made it stand out from other monoelemental nanomaterials. However, along with the research and development, the environmental instability of BP has been found to severely disturb its practical applications. This fact has triggered a number of strategies to improve the environmental stability of BP for its further use. In this review article, we have presented a comprehensive summary of recent progress on research of BP/polymer nanocomposites, including preparation methods, properties, and applications in the optical, biomedical, energy, information storage and flame retardancy sectors. Solution casting, polymerization methods and spinning technology methods are the three main categories of methods to fabricate BP/polymer nanocomposites among the various preparation methods. Benefiting from the encapsulation of different polymers, BP can be well protected in a polymer matrix and some properties can be significantly improved, such as optical absorption, mechanical strength, and environmental stability, which endow a further broad range of investigations of BP. For instance, functionalization of BP with various polymers has been shown to be effective for enhancing the stability of BP based nanomaterials in physiological conditions. More importantly, conjugation of BP with suitable polymers may also enhance the targeting specificity, drug loading efficiency, photo response, and the mechanical properties of BP based nanocomposites, thus significantly promoting the clinical applications of BP in these fields.",
        "category": " Conclusions"
    },
    {
        "id": 29,
        "chunk": "# 6. Challenges  \n\nDespite the above advantages of BP/polymers, there are still many challenges that call for attention. First of all, the preparation methods of BP/polymers should be further optimized, for example, obvious flaws of single crystalline methods are the complex and uncontrollable modification processes of BP. It is necessary to simplify the traditional preparation routes with precise additions of each component. Such precise modulations of BP/polymers with high targeting efficiency, bioimaging capability, and multimodal treatment ability are essential for theranostics of diseases, especially tumors. With proper design of BP/polymer based therapy strategies, the shortcomings of traditional therapy may be overcome. For example, chemotherapy is limited by side effects caused by systematic administration of drugs in a tumor treatment. Loading of chemotherapy drugs onto BP/PEG-FA nanosheets enables tumor targeted delivery and NIR light controlled release of drugs specifically in tumor tissues. Besides, a search for suitable polymers with good fluidity, homogeneity, and large cohesion to prepare BP/polymer spinning fluids is also necessary for the continuous spinning flow and fabricating devices with high-performance. Second, rational selection and utilization of polymers, including the type of polymers, the procedure of functionalization and the thickness of the polymers, is another important issue for improving the stability of BP/polymers. For example, the adjustable stability of BP/polymers is also important for their applications. BP/polymersbased photo electronics exhibits more stable signal output than pristine BP-based devices, which represents a practical aspect. Besides, BP/polymers with relatively high stability are beneficial for reducing the side-effects caused by nonspecific drug release from degradation of the drug carriers, and $\\mathsf{B P}/$ polymers with moderate stability are ideal to support bond regeneration through the sustained in situ supply of phosphorus. Third, BP based mode-lockers exhibit more potential advantages for mid-infrared ultrafast laser systems owing to that the direct bandgap reaches $0.3\\ \\mathrm{{\\eV}}.$ Nowadays, the poor stability can be effectively enhanced by BP/polymers, which will promote the development of BP/polymer mode-lockers in the mid-infrared region. Besides that, most of BP/polymers in ultrafast lasers are used for improving the stability, if the incorporation polymer can promote the properties of BPSA, such as increasing the modulation depth or reducing the response time, it will be useful for the ultrashort pulse generation. Therefore, more research is needed to explore $\\mathsf{B P}/$ polymer mode-lockers. Moreover, a comprehensive investigation of the biocompatibility of BP/polymers is still needed. Much research has been conducted to check the biocompatibility of various BP/polymer nanocomposites, especially those applied in biomedical research. Nevertheless, some of this research is still at its infancy. More comprehensive investigations on BP/polymer-induced acute and long-term effects in the body, especially on the immune, nervous and reproductive systems, is critical for the practical applications of these novel materials. Moreover, a systematic evaluation of the ecological impact of BP/polymers is also urgently needed. Moreover, BP/ polymers have also shown excellent applications in the fields of energy storage, flame retardancy and information storage. Studies on these aspects are ascending, and there are still many areas that need to be further improved. For example, a search for more matching polymers to prepare electrode materials with higher flexibility and stability would be significant for wearable devices. Last but not least, studies of the anisotropy of BP/polymers for their optical, thermal and mechanical properties, and the construction of multifunctional $\\mathsf{B P}/$ polymers constitute promising avenues for new-generation applications.",
        "category": " Results and discussion"
    },
    {
        "id": 30,
        "chunk": "# Acknowledgements  \n\nY.Z., C.M., and J.X. contributed equally to this work. The research was financially supported by the National Natural Science Fund (Grant No. 61905157), Fund of University of South China (Grant No. 201RGC009), Postdoctoral Research Foundation of China (Grant No. 2020M672786), and the Natural Science Foundation of Guangdong Province (No. 2019A1515111060).",
        "category": " Acknowledgements"
    },
    {
        "id": 31,
        "chunk": "# Conflict of Interest  \n\nThe authors declare no conflict of interest.",
        "category": " Conclusions"
    },
    {
        "id": 32,
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Ed. 2014, 53, 5556; c) J. Gu, C. Liang, X. Zhao, B. Gan, H. Qiu, Y. Guo, X.  Yang, Q.  Zhang, D.  Wang, Compos. Sci. Technol. 2017, 139, 83; d) X.  Wang, E. N.  Kalali, J.  Wan, D.  Wang, Prog. Polym. Sci. 2017, 69, 22. [187]\t a) S. Liu, X. Chen, G. Liu, Polym. Int. 2020, https://doi.org/10.1002/ pi.6017; b) Q.  Zhao, Z.  Xie, Y.  Peng, K.  Wang, H.  Wang, X.  Li, H.  Wang, J.  Chen, H.  Zhang, X.  Yan, Mater. Horiz. 2020, 7, 1495. [188]\t J.  Xiong, P.  Cui, X.  Chen, J.  Wang, K.  Parida, M. F.  Lin, P. S.  Lee, Nat. Commun. 2018, 9, 4280. [189]\t Y. Lv, W. Wang, G. Xie, J. Luo, Tribol. Lett. 2018, 66, 61.  \n\n![](images/8153b6944183cb97778ef8470d13a4afd0a249ce2e48252b5cc44c64eb34dc32.jpg)  \n\nYe Zhang received his Ph.D. in applied chemistry at Soochow University in 2018. He is currently a professor in the School of Chemistry and Chemical Engineering at University of South China, Hengyang, China. His research interests focus on the development of novel two-dimensional materials and their derived nanodevices.  \n\n![](images/9e5205ed31c4c7445011a184e162ccaf07f7b4632d2e2233c4292b1afea829e6.jpg)  \n\nChunyang Ma gained his Ph.D. in electronic science and engineering from Jilin University, China. He is now a postdoctor in the Institute of Microscale Optoelectronics, Shenzhen University, China. His research interests concern the nonlinear optical properties of 2D materials and related applications in optoelectronic devices and ultrafast photonics.  \n\n![](images/3bfb3d0bed142c0f4d7f04f56c37be9305d4f8cb39a1d38aaa9e96ef8f030548.jpg)  \n\nJianlei Xie received his Ph.D. from School of Life Sciences at Tsinghua University in 2018. He is now a postdoctor in the Institute of Microscale Optoelectronics, Shenzhen University, China. His research interests focus on the biomedical application of nanomaterials.  \n\n![](images/26a6518765faff6f2ee3c3ec72b819ac28b3fa46b81ce89c567f87566beef8a8.jpg)  \n\nHans Ågren is professor at the Department  of Physics and Astronomy, Uppsala University. His research activities concern molecular/nano/bio photonics and electronics, computational nanoand bio-technology, being a mix of method development and problem-oriented applications.  \n\n![](images/22b713b512c656fb39c33294a7840e95f455088f4b096940948b8e07778660b8.jpg)  \n\nHan Zhang is currently a full professor in the College of Physics and Optoelectronic Engineering at Shenzhen University in China. He is interested in the development of novel two-dimensional materials and their applications in optoelectronics, bio-medicine, and energy storage.",
        "category": " References"
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]