Preparation And Application Of Carbon Quantum Dots Fluorescent Probe

As a kind of fluorescent nanomaterials,carbon quantum dots?CQDs?have been studied by many scholars because of their excellent physical and chemical properties.Its advantages include good light stability,strong biocompatibility and tunable fluorescence emission wavelength.The foreword of this paper mainly introduces several common synthesis methods of CQDs,the progress of surface functionalization of CQDs,and the application of CQDs in energy storage,photocatalysis,biological imaging and detection.In the experimental part,this paper is divided into four parts,to explore the phenomenon that CQDs synthesized from different materials are used as fluorescent probes in biology,food and environment.?1?CQDs with 20.8%quantum yield was prepared by simple heating with citric acid and urea as raw materials.The optimum emission wavelength of CQDs is around 514 nm.The UV absorption peak of Au NPs is at 520 nm,which overlaps with the fluorescence spectrum of CQDs and cause fluorescence quenching.The sulfhydryl?-SH?of cysteine can form stable Au-S covalent bond with gold atom.Keeping the Au NPs away from the CQDs surface and the fluorescence is restored.Based on this,a signal sensor based on CQDs-Au NPs system was established for the determination of cysteine.There is a good linear relationship between the fluorescence intensity and the concentration of cysteine in the range of 0.2-4.0?M,and the detection limit is 0.012?M.?2?CQDs emitting green light were prepared by one-step hydrothermal method,which using citric acid,borax and p-phenylenediamine as raw materials.The fluorescence of CQDs can be quenched by Au NPs.Thiocholine?TC?,which was produced from acetylcholine?ATC?hydrolysis catalyzed by acetylcholinesterase?ACh E?,could induce the aggregation of Au NPs along with a drop in the absorption at 520 nm and result in the recovery of IFE-quenched CQDs fluorescence.When carbaryl was introduced,which inhabited the catalytic activity of ACh E,thus the aggregation of Au NPs and the recovery of CQDs fluorescence was decremented.Therefore,by measuring the fluorescence of CQDs and the absorbance of Au NPs,a double signal analysis method was established to detect carbaryl.This method has high sensitivity and good selectivity.The linear range of fluorescence method is 0.2-150?g/L,and that of colorimetry is 0.2-20?g/L.The double signal detection method has been used to detect carbaryl in water samples with good recovery.?3?In this chapter,a variety of natural products were selected as carbon sources to prepare CQDs by hydrothermal method.After the comprehensive comparison,the waste peel of passion fruit was selected as the carbon source,and the CQDs emitting blue fluorescence were prepared as the fluorescence probe.Based on Fenton reaction,Fe²⁺can effectively quench the fluorescence of CQDs in the presence of H₂O₂.Glucose reacts with glucose oxidase to produce gluconic acid and H₂O₂.Based on the above phenomena,sensitive detection of glucose can be realized.When the concentration is from 0.2?M to 30?M,there was a good linear relationship between the fluorescence quenching degree and the concentration of glucose.The minimum detection limit is 0.09?M,which has been successfully used for the detection of glucose in human serum.?4?The CQDs with good fluorescence properties were prepared from banana peel by hydrothermal method.A new fluorescence ratio sensing platform was established with CQDs as fluorescence probe.When the excitation wavelength of CQDs is 350nm,there is a strong fluorescence emission peak at 3-diaminophenazine?ox OPD?.ox OPD emits yellow fluorescence at 557nm under the same excitation,and the fluorescence of CQDs can be quenched by inner filter effect?IFE?.However,if ascorbic acid?AA?is added,part of Ag⁺will be consumed and dehydroascorbic acid?DHAA?will be generated,which will reduce the content of ox OPD.On the other hand,DHAA and OPD can further inhibit ox OPD production by generating quinoline?DFQ?.The double inhibition will lead to the decrease of yellow fluorescence intensity,while the fluorescence at 440 nm will be enhanced.Therefore,according to the change of fluorescence intensity at 440 nm and 557 nm,a fluorescence ratio platform can be established to determine AA.Under the optimal conditions,the linear range of AA detection is 0.05-50?M,and the detection limit is 0.017?M,which is successfully used in the detection of real samples.