Optical Properties Of Few-layer Black Phosphorus Nanoparticles And Applications In Bio-imaging

Black phosphorus（BP）has attracted much attention as a new member of two-dimensional（2D）materials due to its unique optical and electronic properties and a wide range of promising applications.Since 2014,in optoelectronic field,BP has been reported in applications of ion batteries,photodetectors,modulators,photovoltaic cells,plasmonic devices,gas sensors,and biosensors etc.In biomedical applications,BP is a magical material which can integrate a number of properties within one platform,including photothermal therapy,photodynamic theray,photoacoustic imaging,and drug delivery,etc.Based on BP,in this paper,we produced original research on:1.Synthesis and characterization of BP nano-particles（BPNPs）with a certain lateral and longitudinal size.The as-synthesized BPNPs by using a modified liquid phase exfoliation method have a lateral size of about 35±5 nm,and a thickness of 6±1.5 nm.An ensemble characterization method via transmission electron microscope,atomic force microscope and Raman spectroscopy was conducted.2.Evenly coating a layer of mesoporous silica on the surface of BPNPs,designated as BPNPs@m SiO₂.The thickness of the mesoporous silica is between 8-11 nm.This is an initiative method,which have three significant functions: to improve the dispersibility of BPNPs and prevent BPNPs from agglomerating together;to protect BPNPs from degrading and slow down the rate of BPNPs oxidation;to elongate the photoluminescence lifetime of BPNPs.3.Cytotoxicity and intracellular stability of BPNPs and BPNPs@m SiO₂.Biocompatibility of a nanomaterial is one of the vital indicators for its application value.Therefore different concentrations of BPNPs or BPNPs@m SiO₂ were incubated with human umbilical vein endothelial cells,human embryonic kidney cells（293T）and human breast adenocarcinoma cells（SK-BR3 and MCF-7）for 24 h,48h,72 h,respectively,and assayed using MTS method.BPNPs and BPNPs@m SiO₂ did not show any severe cytotoxicity to the tested human cell lines following 24 h incubation.The stability of BPNPs was studied via Rman mapping methods.Raman spectra of intracellular BPNPs and as-exfoliated material were compared and the data indicated BPNPs were stable in cells.4.Photoluminescence（PL）of BPNPs and BPNPs@m SiO₂.The PL of BPNPs and BPNPs@m SiO₂ was measured with an excitation wavelength of 532 nm using a pulsed laser.The maximum emission was at ⁶90 nm,corresponding to a bandgap of 1.8 e V,which has never been reported before.The 1.8 e V bandgap of the as-exfoliated BPNPs and BPNPs@m SiO₂ is a consequence of combined layer-dependent and size-dependent effects.With the knowledge that BPNPs and BPNPs@m SiO₂ were stable within cells,live cell imaging based on the photoluminescent emission of BPNPs and BPNPs@m SiO₂ was conducted using laser scanning confocal imaging system and two photon imaging system.5.Photoluminescence lifetime（PLT）of BPNPs and BPNPs@m SiO₂.Using a time-correlated single photon counting method,for the first time,we report the PLT of BP nanomaterials and the applications as an efficient agent for PLT imaging.PLT of as-exfoliated BPNPs was 110.5 ps,the PLT of BPNPs@m SiO₂ was 267 ps.With the phenomenon that the PLT of BPNPs is much longer in cells that as-exfoliated BPNPs,we further studied the influence of microenvironment on the PLT of BPNPs.The results indicate that BPNPs are susceptible to its microenvironment.Ionic strength,p H and proteins will influence the PLT of BPNPs.These results are very important.BPNPs can be used as biosensors to probe cancer cells and normal cells since the cellular microenvironment of cancer cells is very different from normal cells.6.The possibility of using BPNPs to realize in vivo two-photon imaging and photoacoustic imaging was explored.According to the experiment results,BPNPs can be applied to in vitro two-photon imaging.The preliminary result of in vivo two-photon imaging was also obtained.Moreover,the as-exfoliated BPNPs have strong photoacoustic signals,while BPNPs@m SiO₂ can provide enhanced photoacoustic signals.This work paves the way for the application of using BP nanomaterials in photoacoustic in vivo imaging.BP is an emerging 2D material,by exploring its unknown optical properties,the application fields will be broadened.In this research,based on few-layer BP,the optical properties of BP nanomaterials and the applications as an efficient agent for live cell imaging are reported.Most imaging agents can only be applied to fixed cells due to their cytotoxicity,which precludes more useful information about the dynamic process of live cells being obtained.As a non-toxic material with high biocompatibility,BP nanomaterials are a new type of ideal imaging agent for live cell imaging.Herein,we researched the principles of BP nanomaterials in different imaging methods and its competitive edges.Solution to one of the biggest challenges,degradation,for the application of BP was come up with.This research lays important foundation for probing live cell via different approaches and leads to promising prospect of BPNPs in multiple biomedical applications.