| With the development of China’s economy,the food industry continues to grow,food safety issues have become prominent.The first premise to ensure food safety is food testing.However,the existing detection methods still have some shortcomings,such as expensive instruments,cumbersome procedures,poor selectivity and so on.Therefore,the development of fast and efficient food detection methods in the field of food safety has very important practical significance.In recent years,the emergence of carbon dot(CDs)provides new ideas and methods for food detection.Because of its superior optical properties,low toxicity and simple preparation method,CDs has a good application prospect in the field of food sensing and detection.In this paper,three kinds of CDs were prepared by electrochemical method,which were used to detect heavy metal ions,ascorbic acid and pH value.The research contents of this paper mainly include the following aspects:1.Yellow fluorescent carbon dots were synthesized by electrochemistry with o-phenylenediamine as carbon source for detection of Fe3+and ascorbic acidUsing o-phenylenediamine as carbon source and sodium chloride solution as electrolyte,yellow fluorescent carbon dots(Y-CDs)were prepared by electrolysis at 10 V for 16 min.The maximum excitation and emission wavelengths of Y-CDs were 261 nm and 570 nm,and the Stokes shift was 309 nm,respectively.The maximum excitation and emission wavelengths were 261 nm and 570 nm,respectively.The Stoker shift is 309 nm.At the same time,the sensitivity of its response to ascorbic acid(VC)and Fe3+was explored.After Fe3+was added,Y-CDs showed new fluorescence emission at 350 nm wavelength,and the fluorescence intensity increased with the increase of Fe3+concentration,while the fluorescence intensity at 570 nm gradually decreased.Based on this phenomenon,a new type of ratio fluorescence sensor was constructed.For quantitative detection of Fe3+,the detection limit is 0.16μM.The selectivity experiment of replacing Fe3+with K+,Cu2+ and Fe2+plasma shows that Y-CDs has the most sensitive response to Fe3+.In the research on the detection of VC by Y-CDs,the fluorescence of Y-CDs before and after the Fe3+treatment can be quenched by VC.Based on this,two methods for detecting VC have been developed,with the detection limits of 0.12 μM and 0.32 μM,respectively.Pyrogallic acid,sodium citrate,tea polyphenols and dithiothreitol had no effect on the determination of VC,so the method had better selectivity for VC.The method was successfully used for the quantitative determination of Fe3+in tap water and VC in beverages.2.Using Congo red as the carbon source to synthesize blue fluorescent carbon dots by electrochemical method to detect pH value and Cu2+Blue fluorescent carbon dots(B-CDs)with maximum excitation wavelength of 356 nm and emission wavelength of 430 nm were prepared by using Congo red as carbon source,sodium chloride solution as electrolyte and electrolysis at 10 V for 20 min.A method for detecting pH value and Cu2+was established.First,the pH value is detected based on fluorescence quenching.In the range of pH=1-5,the standard curve of the detection is:y=-0.184x+0.905,and its R2=0.992.In addition,based on Cu2+can achieve fluorescence quenching detection of copper ions for B-CDs,when the concentration of Cu2+is 0 μM-15 μM,the detection standard curve is:y=0.0126x+0.0127,R2=0.998.After Cu2+is added to B-CDs,the fluorescence intensity increases with the increase of temperature,particle size and Zeta potential increase,which indicates that the fluorescence quenching is caused by the chemical reaction between Cu2+and B-CDs,which is a static quenching method.Finally,the carbon dots were successfully used for the detection of pH value in beverages and Cu2+in tap water.3.Using 1,2,4-Triaminoaniline dihydrochloride as carbon source to electrochemically synthesize red fluorescent carbon dots for pH value determination.Using 1,2,4-triaminoaniline as the carbon source,sodium sulfate solution as the electrolyte,the maximum excitation and emission wavelength of 507 nm and 635 nm were obtained by electrolysis at 10 V for 20 min.The maximum excitation and emission wavelength of R-CDs was 507 nm and 635 nm.The wavelengths of excitation and emission gradually blue shift to 442 nm and 592 nm,respectively.When the pH value is between 5.01 and 6.81,the fluorescence intensity of R-CDs at 592 nm shows a good linear relationship,and the linear equation is y=3.823x-18.586,R2=0.997.In the actual sample test,the pH values of the water samples measured by this method are 6.13,6.39 and 6.37 respectively,while the pH values of the water samples measured by the calibrated pH meter correspond to 6.21,6.36 and 6.51 respectively.The measured values of the two methods are basically the same,which can be better applied to the detection of the pH values of the actual water samples. |
