Rapid Green Preparation Of Nitrogen-doped Fluorescent Carbon Dots And Its Application In Cell/fingerprint Imaging

As a new type of fluorescent nanomaterials,carbon dots?CDs?has attracted extensive attention from researchers in recent years due to its advantages of simple preparation,easy functionalization,excellent optical properties,low biotoxicity and high optical stability.Due to the excellent optical and chemical properties of the CDs,they have a wide range of applications in the fields of bioimaging,biosensing,photocatalysis,optoelectronics,etc.Despite the various synthesis methods to obtain CDs,the bottom-up methods are still the most widely administrated route to afford large-scale and low-cost synthesis.In order to develop high quantum yield and long wavelength CDs,researchers have invested a lot of time and energy.At present,there are some ways to improve the performance of CDs,such as doping or forming complexes with other materials.Generally speaking,doping can effectively improve the quantum yield and optical properties of CDs.In view of the above problems,this paper mainly discusses the synthesis of high quantum yield,long wavelength luminescent CDs and simpler synthesis strategies,and studies their sensing performance to ions,optical film and cell imaging performance.Specific research contents are as follows:1.The N/S co-doped carbon dots?N/S-CDs?was synthesized by one-step microwave using 1,6-hexanediamine dihydrochloride and dimethyl sulfoxide as precursors,and their morphology and structure were characterized by TEM,XRD,XPS and FTIR.The optimal emission wavelength of the CDs was 512 nm with green fluorescence,and was red-shifted gradually as the excitation wavelength aggrandized.The synthesized CDs owned a well quantum yield of 24%.It was further applied for the detection of MnO₄^-and Cr₂O₇^2-with an excellent detection limit of 0.34?M and0.23?M,respectively.Cr₂O₇^2-did not influence the N/S-CDs PL response of MnO₄^-in the presence of excessive Pb²⁺.Moreover,the obtained N/S-CDs demonstrated preeminent biocompatibility and could be resoundingly applied for cellular imaging.2.Blue emissive N-doped CDs with QY of 83%and orange emissive N-doped CDs with QY of 47%were successfully prepared using resorcinol and phloroglucin as carbon resource in formamide by one-step microwave synthesis,respectively.Formamide not only plays a role as solvent but also takes part in the formation of the high QY CDs.Through the characterization of XPS and FTIR,it is proved that a large number of functional groups exist on the surface of CDs,such as-COOH,-NH₂,-OH.It is demonstrated that the as-prepared blue-and orange-emitting N-doped CDs with high QY can be uniformly dispersed into glue and be fabricated as CDs/glue fluorescent composites for fluorescent film and fingerprint imaging.Furthermore,these CDs also show excellent cellular imaging capability.3.We report an ultrafast,simple and energy-free method for ultrafast synthesis of CDs.The CDs could be synthesized within seconds by directly mixing bromoacetonitrile with 1-methylimidazole or 1-vinylimidazole without any auxiliary equipment at room temperature.Such obtained CDs exhibit excellent fluorescence performance and photoluminescence stability.As the excitation wavelength increased,the emission peaks of the obtained CDs were red-shifted,and the emission reached the orange fluorescence of 550 nm.The quantum yield?QY?of two synthesized CDs was16%and 21%,respectively.The fluorescence emission intensity,further,remained unchanged after 350 minutes under 365 nm continuous UV irradiation.In addition,the high survival rate of HUVEC cells?87%?indicates that CDs have low cytotoxicity and excellent biocompatibility,boding well for their widespread applications in cell imaging.