Synthesis Of Red Fluorescent Carbon Dots And Their Applications In Sensor Analysis And Cell Imaging

Carbon dots(CDs)as a kind of luminescent nanomaterials have the advantages of simple preparation method,stable optical and chemical properties,low cytotoxicity,and good biocompatibility,which have been widely used in cancer treatment and other fields.Among them,long-wavelength-emitting CDs also have high tissue penetration,low tissue damage and strong anti-body autofluorescence,which are more conducive to the biological imaging of CDs.However,the structure of CDs is ever-changing due to the different preparation methods and various precursors and it is difficult to obtain a unified mechanism to guide the preparation of CDs.The current study shows that both the doping of heteroatoms and the enlargement of the carbon-nucleus conjugated domains can cause the changes in the band gaps and energy levels of CDs,leading to the red-shift of emission wavelengths.Based on the above questions and inspirations,the following research is carried out:A highly efficient fluorescent nanoprobe based on red-emitting carbon dots(R-CDs)was prepared by a facile solvothermal method.The emission wavelength of the as-prepared R-CDs located at 627 nm when the excitation wavelength was 560 nm and showed excitation-independent emission as the excitation wavelength was changed from 480 nm-570 nm.Further studies revealed that the formation of new surface states by N and S doping and the formation of large conjugated systems by dehydration and carbonization were the main reasons for the red shift of fluorescence.The fluorescence intensity decreased significantly after adding Cr₂O₇^2-to the R-CDs solution,realizing the specific selection of Cr₂O₇^2-and the detection limit was as low as 79.00 n M.Meanwhile,the obtained R-CDs could enter He La cells through endocytosis and showed bright red fluorescence under confocal scanning microscope,displayed that R-CDs had excellent cell imaging capabilities.Three different color emission carbon dots(b-CDs,o-CDs,r-CDs)were prepared by changing the reaction solvent(acetic acid,water and sulfuric acid)using o-phenylenediamine as a precursor.Through the detailed characterization of the three CDs structures explored the effect of solvent change on the emission wavelength of CDs.It can be seen that the change of the crystallization degree of CDs by changing the solvent was the reason of the fluorescence emission wavelength of CDs shifts from blue to orange.The red shift of CDs emission wavelength from orange to red was due to the addition of sulfuric acid,which can increase the conjugated domain of the carbon core.Further investigation showed that the R-CDs obtained by optimizing r-CDs had the advantages of good chemical stability,excellent optical properties and low cytotoxicity.The fluorescence of R-CDs showed an on-off process after adding Fe³⁺by forming non-fluorescent compounds,which realized the specific recognition of Fe³⁺with a detection limit of 194 n M.The experimental results show that R-CDs can be successfully used for the detection of Fe³⁺in tap water,urine,serum and HeLa cells.