Applications Of Graphene Quantum Dots In Food Additive Quantitative Analysis

In recent years,food safety has become a hot issue of social concern.There are many chemicals in life that will bring harm to human health,such as food additives and pesticide residues in vegetables and fruits.To safeguard food safety and protect the legitimate rights and interests of consumers,it is necessary to establish a fast and efficient method for detecting food additives.The current research focus is to develop simple,efficient,and low-cost detection methods for food additives.Fluorescence spectrometry has the advantages of simple operation,fast response,high sensitivity,and good selectivity,which has been widely used in analytical research.In this thesis,nitrogen-doped graphene quantum dots(N-GQDs)and nitrogen-sulfur-doped graphene quantum dots(N,S-GQDs)that could be quenched/ enhanced by food additives were selected for study,which would be used for the quantitative analysis of food additives,with the advantage of fast,low cost,simple operation and high sensitivity,and laid a foundation for relevant research.The research contents are summarized as follows:1.Nitrogen-doped graphene quantum was used as off-on fluorescent probe for quantitative analysis of BSAStudy showed that the formation of complex of alizarin red and N-GQDs could effectively quench the fluorescence intensity of N-GQDs,named fluorescence quenching(off).Alizarin red can interact with Arg-193,Arg-255,Lys-220,Arg-197,and Ala-289 residues on BSA through hydrogen bonds,which could be replaced from alizarin red nitrogen-doped graphene quantum dots complex system,induced recovery of fluorescence of nitrogen-doped graphene quantum dots(on).Above all,an off-on fluorescence method for quantitative analysis of BSA has been established,with the limit detection of 0.011 g/L.This method has also used for quantitative analysis of BSA in urine samples with recoveries of 99.3 %-99.6 %.2.Application of single wavelength nitrogen-sulfur doped graphene quantum on quantitative analysisResults showed that both Mn and Cu ions could effectively quench the fluorescence of N,S-GQDs,and quenching progress induced by Mn ion is dynamic quenching process,while for Cu ion is static quenching process.The lowest limit detection of this method for Mn and Cu ions could reach 3.042 μmol/L and 2.708 nmol/L,respectively.This method has also been used for quantitative analysis of Cu ion content in wine with recoveries of 102.4 %-113.7 %.Moreover,the interaction between malachite green and N,S-GQDs has also been studied,which was a static quenching process,and the lowest limit detection could reach 4.83 nmol/L.This method has been used for quantitative analysis of malachite green in water sample with recoveries of95.80 %-116.30 %.3.Application of ratiometric fluorescence method on quantitative analysis of malachite greenSingle wavelength fluorescence quenching method would be easily affected by environment,light intensity,noise,and other factors.But ratiometric fluorescence method with dual wavelength as the monitoring system could effectively improve the above shortcomings,such as improving the signal-to-noise ratiometric,sensitivity and accuracy of measurement.A ratiometric fluorescence system has been successfully constructed,based on N,S-GQDs and Cd Te quantum dots as fluorescent nanomaterials,and both quantitative analysis and visual detection of malachite green have been realized.For quantitative analysis,the lowest limit detection could reach 0.4597 nmol/L,while the concentration of visual analysis was 16.44μmol/L(fluorescence changed from red to blue).This ratiometric fluorescence method has successfully used for quantitative analysis of malachite green in water sample with recoveries of99 %-100 %.