Preparation Of Carbon Dots And Their Fluorescence Sensing

Carbon dots(CDs)is a kind of zero-dimensional carbon nanometer material.Due to its small size,it shows special properties that the original macroscopic materials do not equipped.This kind of material often has the advantages of easy tubulization,adjustable energy band structure,low cytotoxicity,high water solubility and dispersibility.After more than a decade of development,CDs is widely used in sensor analysis,catalysis,photoelectric devices,biological imaging and diagnosis,information encryption and anti-counterfeiting,and energy storage.More research focuses on the regulation of CDs size,surface functional groups,precursor selection and synthesis methods in order to prepare CDs with wide p H range,long emission wavelength and high fluorescence quantum yield(PL QY)and broaden its application field.In this paper,CDs with high PL QY and excellent fluorescence performance was prepared by a simple synthesis method,and its application in biosensor analysis was mainly explored.The mainly contents are as follows:(1)Carbon dots(d-CDs and f-CDs)were synthesized from liquid fuels rich in aromatic carbon compounds by chemical oxidation,and their application in the detection of copper ions(Cu²⁺)in rat brain microdialysate was carried out.According to the composition of the precursor,the prepared CDs showed different morphology and photoluminescence characteristics.At the same time,d-CDs has a high selectivity to Cu²⁺,and can recognize Cu²⁺significantly even in the presence of other interferences.Cu²⁺can cause obvious fluorescence quenching of d-CDs,and the change of fluorescence intensity of d-CDs shows a good linear relationship with the concentration of Cu²⁺(0-4?M),and the low detection limit(LOD)is 0.039?M.According to this characteristic,we used d-CDs as a fluorescence sensing platform to conduct online analysis of Cu²⁺in vivo.The results showed that the basic value of Cu²⁺in rat brain microdialysate was about 2.82±0.16?M(n=3),which was consistent with the reported values.(2)We employ 3D nitrogen-doped porous graphene frameworks(3D NPG)as raw material to prepare emissive nitrogen doped graphene quantum dots(r-NGQDs)via chemical oxidation method.The as-prepared fluorescent r-NGQDs was integrated with Co OOH nanosheets to construct a sensing platform for in vivo ascorbic acid(AA)analysis.Initially,the fluorescence emission intensity of r-NGQDs was quenched by Co OOH nanosheets based on the inner filter effect(IFE).Then the quenched intensity of r-NGQDs and Co OOH nanosheets system was enlightened by the addition of AA,since AA could consume Co OOH nanosheets through redox reaction,leading to the release of r-NGQDs and fluorescence restoration.Moreover,the restored fluorescence intensity of r-NGQDs is highly dependent on the concentration of AA which endows them as a quantitative analysis of AA with a LOD reach up to1.85?M(n=3)in aqueous solution.Finally,the as constructed bionanosensor was further employed for in vivo analysis of AA in living rat brain microdialysate with basal value up to 9.4±1.4?M(n=3).(3)Taking rhodamine B(RhB)and urea as carbon source and nitrogen source,the multicolor luminescent CDs was prepared in one-step by simple hydrothermal synthesis.Three typical colors CDs were obtained by column chromatography separation and purification:blue(b-CDs),green(g-CDs)and yellow carbon(y-CDs).The CDs has strong fluorescence stability,wide p H range,good water solubility and dispersion.TEM,XPS,FT-IR and other characterization analysis showed that the particle size,functional groups structure and nitrogen content of different emission CDs were different,and the content of amino nitrogen increased significantly from b-CDs,g-CDs to y-CDs.Different absorption functional groups and emission wavelength were found by UV-vis and fluorescence spectroscopy.The absolute quantum yield was 11.1%,34.8%and 22.9%,respectively.A series of characterization data indicate that the redshift mechanism of emission wavelength may be caused by the difference of nitrogen content.In addition,the obtained CDs have good hypochlorous acid(HCl O)response.The addition of HCl O can significantly quench the fluorescence of CDs,and the change of fluorescence intensity is linear with the wide concentration of HCl O.This is due to HCl O oxidizing CDs surface functional groups,reduce the electron density resulting in fluorescence quenching.Moreover,these CDs have low cytotoxicity and good biocompatibility,and were successfully applied to cellular imaging.