Preparation Of Fluorescent Carbon Dots And Their Applications In Ion Detection And Cell Imaging

Carbon dots was a new type of fluorescent carbon nanomaterials with excellent optical properties and low toxicity compared to traditional fluorescent materials,which have irreplaceable advantages in the field of sensing.It is important to further explore the functionalized synthesis method of carbon dots and expand their applications in the fields of analytical detection and bioimaging.In this paper,two functionalized fluorescent carbon dots were prepared by solvothermal method,designed with nitrogen doping and polymer modification strategies,and finally applied as fluorescent probes for the detection of Cu²⁺in water and targeting A549 lung cancer cells imaging,respectively,as follows:Nitrogen-doped blue fluorescent carbon dots B-CDs were synthesized in formamide solvent using citric acid as the carbon source and introducing ethylenediamine as the nitrogen source.The reaction temperature,time and mass ratio of raw materials were investigated by single-factor experiments,and the optimal preparation conditions were determined as follows:solvent heat reaction temperature of 180℃,reaction time of 4 h,and the mass ratio of citric acid and ethylenediamine of 1:4.The prepared B-CDs have non-excitation wavelength-dependent optical properties with an optimal excitation wavelength of 400 nm and an emission peak located at 476 nm,with a relative fluorescence quantum yield of about 10.28%.The morphology,chemical structure and optical properties of the B-CDs were characterized and analyzed.The prepared B-CDs are monodisperse nanoparticles with good fluorescence stability and have the ability to be applied in complex detection environments.The morphology,chemical structure and optical properties of the B-CDs were characterized and analyzed.The prepared B-CDs are monodisperse nanoparticles with good fluorescence stability and have the ability to be applied in complex detection environments.A fluorescence sensing system was developed for the highly sensitive detection of Cu²⁺based on static bursting and photoelectron transfer.The linear ranges were 0.25μM-4.5μM and 0.45μM-10μM with a minimum detection limit of 0.18μM.The method was successfully applied to the determination of Cu²⁺content in laboratory tap water and river water of the Hunhe River.Nitrogen-doped red fluorescent carbon dots R-CDs were synthesized in N,N-dimethylformamide solvent using citric acid as the carbon source and urea as the nitrogen source.The emission wavelength of R-CDs was 620 nm and the fluorescence quantum yield was 12.89%.Because its surface is rich in reactive amino groups,it can be directly covalently cross-linked with the carboxyl group of hyaluronic acid（HA）to form CD44 receptor-targeting fluorescent carbon dots HA-R-CDs,and the successful modification of hyaluronic acid-targeting molecules was characterized by infrared spectroscopy and zeta potential.The cytotoxicity of R-CDs and HA-R-CDs on A549human lung cancer cells was evaluated by MTT cytotoxicity assay,which showed that both red light carbon dots exhibited low cytotoxicity and good biocompatibility in the range of 0-60μg/m L.The imaging performance of R-CDs and HA-R-CDs was compared by fluorescence microscopy imaging.Although the fluorescence intensity of HA-R-CDs aqueous solution was lower than that of R-CDs,HA-R-CDs showed a brighter red fluorescence than R-CDs inside the cells,which indicated that HA-R-CDs were successfully internalized in lung cancer cells in a CD44 receptor-mediated manner within a shorter period of time（40 min）.