Preparation Of Novel Fluorescent Carbon Dots And Their Application In Sensing,Bioimaging And Antibacterum

Objective:As a new type of carbon nanomaterial,carbon dots show excellent optical properties,low toxicity and good biocompatibility,which makes it a good application prospect in the biological field.Due to the low yield of fluorescence quantum,the optical properties of carbon dots will be affected.However,the application of short-wavelength carbon dots with background fluorescence in biological imaging will be limited.In order to broaden the application range of carbon dots,it is very meaningful to preparate carbon dots of high fluorescence quantum yield and long-wavelength luminous in biological applications.The work of this paper is as follows:1.Using L-tartaric acid and triethylenetetramine as raw materials,the blue fluorescent nitrogen-doped carbon dots with high fluorescence quantum yield(23%)were synthesized by one-pot microwave method,and the the optimization of reaction ratio is 1:1.The QY is 23%,which is higher than the average carbon dots.2.Based on the first chapter,the sensing experiments of as-prepared N-CDs were investigated,and applied to the detection and cell imaging of metronidazole.3.Using water-soluble melanin and betaine hydrochloride as carbon sources,the red-fluorescent carbon dots with fluorescence quantum yield of 6.5% were synthesized and applied to cell imaging,zebrafish imaging and bacteriostasis research.Methods:1.The nitrogen-doped carbon dots with high fluorescence yield were synthesized using L-tartaric acid and triethylenetetramine as precursor by one-pot microwave method.The structure and optical properties of N-CDs were determined.Transmission electron microscopy was used to characterize the morphology and particle size,and X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to to characterize the functional groups.The optical properties of N-CDs were characterized by ultraviolet-visible absorption and photoluminescence spectra.2.Through the interaction of N-CDs with different substances,the effects of different substances on the fluorescence properties of N-CDs were explored.Using human breast cancer cells(MCF-7)as a model,MTT assay was used to detect the cytotoxicity of N-CDs.And the imaging experiments of N-CDs in cells were performed by laser confocal microscopy.3.Using water-soluble melanin and betaine hydrochloride as raw materials,red-emitting carbon dots were synthesied by one-pot hydrothermal.The structure and composition of the synthesized R-CDs were characterized by transmission electron microscopy,Fourier transform infrared spectroscopy,X-ray diffraction and X-ray photoelectron spectroscopy.The optical properties of R-CDs were determined by ultraviolet-visible absorption spectra and photoluminescence spectra.The antibacterial effect of R-CDs was studied by the interaction of R-CDs with three common bacteria.Results:1.The structural characterization of the synthesized N-CDs showed that the N-CDs were quasi-spherical with a particle size range of 1-5 nm and an average particle size of about 2.56 nm.The surface of N-CDs contained water soluble group such as hydroxyl groups,carboxyl groups and amino groups.The effect of different factors on the optical properties of the synthesized N-CDs was determined.The experiments have shown that the optical properties of the synthesized N-CDs are stable.In summary,the N-CDs have good water solubility,high fluorescence quantum yield(23%)and excellent photostability.2.The N-CDs have high sensitivity to metronidazole,and the drug metronidazole can be effectively detected by fluorescence quenching.The detection limit is 0.22 μmol/L.The results of MTT assay showed that the cytotoxicity of N-CDs was low,and it was successfully applied to the detection of metronidazole in the actual sample(milk).Finally,this phenomenon is used to detecte the presence of metronidazole in cells by fluorescence quenching.3.The structural characterization of the synthesized R-CDs showed that the R-CDs were quasi-spherical with diameters of 4-5 nm,and the average particle size is about 4.32 nm,and the surface contains hydroxyl groups and carboxyl groups.Experiments on the optical properties of the synthesized R-CDs show that R-CDs have good optical stability.Laser confocal microscopy was used to study the imaging of R-CDs in human breast cancer cells(MCF-7)and zebrafish.Finally,the antibacteria assay of R-CDs against E.coli,Proteobacteria and Staphylococcus aureus was determined.The results showed that R-CDs could effectively kill E.coli.In summary,the synthesized R-CDs have excellent optical properties,low cytotoxicity and good biocompatibility,can be well applied to biological imaging,and have strong antibacterial effects against E.coli.Conclusion:In this paper,two carbon dots(N-CDs and R-CDs)were synthesized simply and rapidly by optimizing the synthesis conditions,and as-prepared N-CDs have excellent photoluminescence properties,low toxicity and good biocompatibility.The as-prepared N-CDs show sensitive detection for small molecule drug metronidazole,which is applied to determine metronidazole of actual milk sample and cell,and the results are reliable.The R-CDs can emit strong fluorescence at 650 nm,which have been successfully applied to cells and living images.The antibacterial experiments show that the R-CDs can effectively kill E.coli,and the effect is obvious.