Preparation Of Bifunctional Carbon Quantum Dots And Their Applications In Colorimetry And Fluorescence Analysis

Carbon quantum dots(CQDs)are a new type of carbon nanomaterials with stable optical properties,good biocompatibility and no toxicity,showing widely applications in the fields of chemical and biological sensing and imaging.Biomass is a kind of green and economic raw material,which is rich in C and other atoms(such as O,N,S,etc.),and it is an ideal carbon source for the preparation of CQDs.In this paper,biomass as carbon source,using one-step hydrothermal method to prepare the bifunctional CQDs with the characteristics of peroxide-mimicking enzyme and fluorescence emission,and used to construct methods for biothiol,glucose and uric acid.The specific contents are as follows:(1)CQDs were prepared by hydrothermal method using chicken blood as carbon source.The morphology of CQDs were characterized by transmission electron microscopy,the CQDs were approximately spherical,with good dispersion,and the particle size was between 1.5 and 3.6 nm,the average diameter was about 2.4 nm.These CQDs could catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine(TMB)in the presence of H₂O₂ to generate the blue oxidation product(ox-TMB),which showed a strong absorption peak at 652 nm.However,the addition of biothiol could inhibit the formation of ox-TMB,the blue color fades and the absorbance decreases.On this basis,a highly selective and sensitive colorimetric method for the determination of biothiols was established,and it was applied to the determination of cysteine(Cy SH)in human serum with recoveries of 91.5%-109%.(2)Fluorescent CQDs with catalytic activity were prepared by hydrothermal method using pig liver as carbon source and used for the colorimetric determination of glucose.The principle is that under the catalysis of glucose oxidase(GOx),glucose was oxidized to produce H₂O₂;CQDs further catalyzes H₂O₂ to oxidation of TMB produce blue ox-TMB.Under the conditions of pH 3.5,temperature 40?,200?L CQDs and 2.0 mM TMB,the glucose concentration was in the range of 10.0-200?M,it showed a good linear relationship with A₆₅₂,and the detection limit was 0.87?M.The method was applied to the determination of glucose in human serum with recoveries of 95.8%-103%.(3)A colorimetric and ratiometric fluorescence dual-signal method was established for the detection of uric acid.The prepared CQDs could catalyze the oxidation of o-phenylenediamine(OPD)by H₂O₂ to produce the yellow2,3-diaminophenazine(DAP),which exhibited obvious absorption peak at 420nm and strong fluorescence emission peak at 550 nm.Due to the fluorescence spectrum of CQDs overlaps with the absorption spectrum of DAP,DAP quenches the fluorescence of CQDs through internal filtering effect(IFE).The results showed that with the increase of uric acid concentration,the absorbance of DAP at 420 nm and the fluorescence intensity at 550 nm increased,whereas the fluorescence of CQDs at 450 nm decreased.Therefore,the concentration of uric acid could be analyzed by measuring the absorbance at 420 nm and fluorescence intensity ratio(I₅₅₀/I₄₅₀).The method was used to analyze the content of uric acid in human urine,and the results of the colorimetric and ratiometric fluorometric assays were basically consistent with recoveries of94.0%-105%.(4)Fe,N co-doped carbon dots(Fe,N-CQDs)were prepared by hydrothermal method using leaf of syngonium podophyllum schott,ammonium ferric sulfate dodecahydrate and urea as raw materials,and their morphology,elements and groups composition were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy and fourier transform infrared spectroscopy.Their particle size was between 1.34 and 3.68 nm,the average diameter was about 2.51 nm.It also indicates that Fe and N elements were successfully doped into CQDs,and there were abundant O-and N-containing functional groups on the surface.The Fe,N-CQDs possessed both peroxidase-like activity and strong fluorescence emission at 450 nm.Using Fe,N-CQDs and OPD as probes,a dual-signal method for glucose was established.Under the conditions of p H 5.4,temperature 40°C,1.75 m M OPD and reaction time 25 min,A₄₂₀ and I₅₅₀/I₄₅₀ showed a good linear relationship with glucose concentration in the range of 1.0-100?M,respectively.The method was used for the determination of glucose in human serum with recoveries of 93.3%-112%.