Application Of New Fluorescence Sensor Based On Carbon Dots In Detection Of Active Substances

Carbon dots（CDs）,an emerging zero-dimensional carbon-based nanomaterial with a size less than 10 nm,which not only has excellent fluorescence properties,but also has many reaction sites and functional groups on the surface due to the special structure.CDs can change the fuorescence intensity through the interaction of surface groups or modified reaction sites with the analyte,thereby the analyte can be qualitatively and quantitatively detected.In addition,CDs also have the advantages of good water solubility,environmental friendliness,widely raw materials,low toxicity and good biocompatibility.The assay of using fluorescent CDs for detection has the advantages of high sensitivity,rapid response,good selectivity,real-time detection and easy operation.There have been already many reports about the appications of CDs,such as food and environmental detection,biochemical sensing,bioimaging,drug delivery and so on.However,the applications of CDs-based sensors in metal ions detection are far more than the detection of other substances.Therefore,there is still huge potential for exploration in the detection of active substances.This thesis attempts to design,synthesize and modify different CDs for the detection of active substances.The specific researchs and results are as follows:（1）The CDs were successfully prepared by hydrothermal method using catechol as a single carbon source.The synthesis method is simple and does not require complex post-processing procedures such as passivation,doping and modification.The proposed CDs have excellent water dispersibility,good fluorescence stability and higher quantum yield（32%）than other reported non-modified and non-doped CDs.By performing a series of characterizations on the prepared CDs including TEM,FTIR,UV-Vis,PXRD,XPS,it was found that the fluorescence of CDs could be quenched with hypochlorite（Cl O^-）by oxidation of the residual pyrocatechol groups on the surface to o-benzoquinone.The photostability,p H stability,selectivity and strong ion concentration stability of CDs were studied in detail.We established a new method for the analysis of Cl O^-.The assay covered a linear range from 0.1 to 10μM with a low detection limit of30 n M and it was successfully applied to the detection of Cl O^-in real tap water.（2）Firstly,NBD piperazines（NBD-P）were prepared by organic synthesis,then blue-emitting CDs were synthesized using citric acid as carbon source.CDs are energy donors,NBD are energy acceptors and piperazine are reaction sites.The CDs and NBD-P were connected by a simple stirring adsorption to construct a fluorescence resonance energy transfer system（FRET）.The synthesis ratio and reaction conditions were optimized,and the fluorescence properties,surface groups and elemental composition of the modified CDs were studied in detail.The modified CDs showed excellent selectivity and sensitivity to H₂S,showing a good linear relationship in the range of 1-90μM with 0.21μM limit of detection.The method was successfully applied to the imaging analysis of endogenous and H₂S in MCF-7cells,and the changes of fluorescence intensity caused by exogenous H₂S can be visually observed from the bioimaging,which provides a new approach to the study of physiological and pathological process associated with H₂S concentration.（3）B-doped CDs（B-CDs）were prepared by hydrothermal method using catechol as carbon source and phenylboronic acid as boron source under a certain concentration of sodium hydroxide.The B-CDs showed weak or even no fluorescence,and the fluorescence intensity of B-CDs was enhanced after the addition of H₂O₂.Therefore,a new assay of fluorescence“turn on”based B-CDs detecting for H₂O₂ was established.The ratio of raw materials,the concentration of sodium hydroxide and the experimental reaction conditions were optimized.The elemental composition of the B-CDs and the changes in surface groups,UV absorption and fluorescence properties before and after reaction with H₂O₂ were studied.The selectivity and sensitivity of B-CDs to H₂O₂ were also studied.There was a good response between B-CDs and H₂O₂ in 0.05-3 m M,and the limit of detection was 28μM.The method was successfully applied to the spike detection of tap water and goat serum,which shows good accuracy and reliability.