Synthesis Of Nitrogen-Doped Two-Dimensional Black Phosphorus Materials And Their Application In Tumor Treatment

Malignant neoplasms are an international health challenge that poses a significant threat to human health.Chemotherapy is an effective treatment for cancer,but chemical drugs can be toxic to normal cells.Therefore,the development of a safer and more efficient nanoplatform for tumor diagnosis and treatment will be a boon to cancer patients.Among them,optical therapy has the advantages of less damage,less harm and less side effects,and its treatment principle is to produce single linear oxygen（¹O₂）or generate high temperature under specific light to kill tumor cells.Meanwhile,among the two-dimensional nanomaterial family,black phosphorus（BP）has excellent biodegradability and biosafety,which can effectively reduce the harm to living organisms and thus provide safer and more effective treatment methods for patients.Unfortunately,there are still relatively few studies on fluorescence imaging of BP in the tumor microenvironment,which can label cells and record the changes of cells.Based on this,multicolor fluorescent black phosphorus nanosheets（N/BPNs）were prepared by doping black phosphorus nanosheets with different contents of nitrogen elements based on the solvent thermal method to prepare blue fluorescent black phosphorus nanosheets（BPNs）,and then the principle of photodynamic-photothermal therapy was used to inhibit tumor growth by synergistic 660 nm laser induction.Firstly,transmission electron microscopy（TEM）and atomic force microscopy（AFM）are used to characterize the lateral size,thickness and morphology of the prepared materials.The fluorescence spectrophotometer（FL）analysis of multicolor fluorescent black phosphorus nanosheets was consistent with the fluorescence phenomenon under 365 nm UV lamp and405 nm laser,and the absorption peak of the UV absorption spectrum at 218 nm proved that the doping did not adversely affect the black phosphorus itself.Fourier transform infrared（FT-IR）spectra and X-ray photoelectron spectroscopy（XPS）showed that different degrees of oxidation of black phosphorus surface caused by different nitrogen contents were important reasons for the redshift of fluorescence.At the same time,the fluorescence stability of BPNs and N/BPNs under different p H environments,1,3-diphenylisobenzofuran（DPBF）degradation experiments and electron spin resonance（ESR）results showed that the prepared multi-colored black phosphorus nanosheets not only had good stability,but also generated ¹O₂under visible light,and the generation rate increases with the wavelength gradient,which had excellent photodynamic characteristics.Next,the biosafety of materials,the tracer effect of cell imaging,and the therapeutic effect of tumors treated with different materials without laser irradiation or with laser irradiation were explored.Firstly,the cytotoxicity level and the physiological indicators of the mice after tail vein injection were normal,which confirmed the biological safety of the material.Then,liver cancer cells were treated with the same concentration of BPNs and N/BPNs,and obvious blue fluorescence,green fluorescence,yellow fluorescence,orange fluorescence and red fluorescence appeared in the cells,which achieved the effect of tracing and labeling cells.Finally,a mouse tumor model was constructed,and after a 14-day treatment cycle,the mice in the material group showed a certain effect of tumor inhibition.After the addition of laser,the material groups showed a more obvious inhibition effect,among which R-N/BPNs had the best therapeutic effect.In summary,the prepared BPNs and N/BPNs not only have excellent optical properties,but also show great potential for application in the treatment of tumors.