| In recent years,nanomaterials have been widely used in many fields such as biology,food and medicine and environment detection due to their stable physicochemical properties,excellent size effect and diversity of synthetic methods.Among these common nanomaterials,carbon quantum dots is favored by researchers because of their advantages of small particle size,excellent water solubility,stable optical properties and excellent biocompatibility.At present,using carbon quantum dots as fluorescent probes,various simple methods have been developed to detect trace components in food system,such as ions,functional small molecules and organic macromolecules.In this paper,two kinds of doped carbon quantum dots with stable properties and excellent optical properties were synthesized by different methods respectively,and they were designed as fluorescent probes and applied to the analysis and detection of food substances.The specifi c contents are as follows:(1)The nitrogen-sulfur co-doped carbon quantum dots(N.S-C Ds)emitting blue fluorescence and nitrogen doped carbon quantum dots(N-CDs)emitting yellow-green fluorescence were prepared by microwave assisted method and hydrothermal method respectively.The optical properties,structures and morphologies of the two carbon quantum dots were systematically analyzed by various characterization methods.The results show that the doped carbon quantum dots prepared by two different methods have excellent water solubility,stable fluorescence performance,good dispersion and uniform size.(2)Based on the fluorescence characteristics of the synthesized N.S-CDs,a"closed-open" fluorescent probe was constructed for the highly sensitive detection of ascorbic acid(AA)by combining with Fe3+.According to the research,Fe3+ can quench the fluorescence of N.S-CDs by electrostatic quenching mechanisru,but in the presence of ascorbic acid,Fe3+ can be reduced to Fe2+,which inhibits fluorescence quenching and the fluorescence is restored,so as to realize the detection of ascorbic acid.Under the optimal experimental conditions,the limit of detection of 2.31?mol/L for AA was obtained over a linear range for 10 to 150 ?mol/L.At the same time,the method was successfully applied to the determination of ascorbic acid in fruits and obtained satisfactory results with the recovery range of 93.12-106.89%.In this work,the fluorescence sensor system constructed by carbon quantum dots has simple and eco-friendly synthesis processes,is rapid,and has high detection efficiency.Therefore,such a switch-on sensors may be a promising candidate sensor for AA detection in fruit samples.(3)A simple,sensitive and highly selective method for the determination of alkaline phosphatase(ALP)activity based on internal filtering effect(IFE)was established by using N-CDs as fluorescent probe,which prepared by the above hydrothermal method.The substrate p-nitrophenylphosphate(PNPP)is hydrolyzed under the catalysis of ALP,and the product p-nitrophenol(PNP)is a kind of strong light-absorbing substance.Its maximum absorption wavelength can well overlap with the excitation wavelength of the prepared N-CDs,and the competitive absorption significantly weakens the excitation of N-CDs,resulting in the effective quenching of N-CDs.Under the optimal conditions,there is a linear relationship between the fluorescence quenching degree of N-CDs and the activity of alkaline phosphatase,the limit of detection of 0.037 U/L for ALP was obtained over a linear range for 0.05 to 10 U/L,the detection limit is lower than most detection methods previously reported.The fluorescence probe has the advantages of simple,sensitive,high selectivity and low dosage,and has been successfully applied to the determination of alkaline phosphatase in serum of domestic animals.In this work,the presented detection method base on IFE which doesn't require complex modification of the fluorophen,would open a new avenue for simple and rapid detection of enzyme activity,and is expected to be applied to the construction of new fluorescence detection platforms. |
PDF Full Text Request