Preparation Of Carbon Nanodots And Their Applications In The Detection Of Food Hazard Factors

With the rapid development of industrialization,food safety accidents emerge endlessly.Heavy metals,chemical additives,harmful small molecules and other pollution will pose potential harmful effects on human health.The detections of these pollutants by traditional large-scale instrument detection are difficult to be widely extended,which is not conducive to food safety control.Therefore,it is urgent to construct a fast,efficient,convenient and cheap detection method.As a new type of fluorescent nanomaterial,carbon dots have more possibilities in the field of food detection due to its adjustable size,fluorescence emission wavelength regulation and high photoluminescence efficiency.In this paper,three new carbon dots(CDs)were synthesized using phosphate buffer(PBS)as electrolyte based on electrochemical method,and the detection application was carried out for food safety hazard factors(nitrite,chromium VI,sodium hypochlorite).The main contents are as follows:1.Blue strongly fluorescent naphthalene ethylenediamine carbon dots(NETHCDs)are obtain by electrolysis at 10 V voltage and used for the detection of nitrite by fluorescence and colorimetric dual sensing,using naphthalene ethylenediamine as carbon source and PBS as electrolyte,the excitation wavelength of NETH-CDs is 359 nm,the emission wavelength is 431 nm and the average particle size is 2.59 nm.The structure and chemical properties of NETH-CDs are characterized by Raman spectroscopy,Fourier infrared spectroscopy and X-ray photoelectron spectroscopy.Based on the Griess reaction principle,NETH-CDs can realize the fluorescence and colorimetric dual sensor application of NO2-in the range of 0.2-100μm.The absorbance at 538 nm is linear to NO2-in colorimetric sensing,ΔA=0.0088+0.0097Cnitrite(R2=0.998;LOD=0.1 μM);In the application of fluorescence sensing,when the excitation wavelength is 359 nm,the fluorescence intensity of NETH-CDs changes upon NO2-concentration.ΔF/F0=0.0053+0.028Cnitrite(R2=0.996;LOD=0.08 μM),when NO2-at 300 μM results in complete quenching of CDs fluorescence.Finally,NETH-CDs was applied to NO2-detection of ham and pickle.The results show that the recovery rate was 98.6-102.8%,and the relative standard deviation(RSD)is less than 3.34%.According to temperature test,fluorescence life and Zeta potential,the fluorescence sensing mechanism is dynamic quenching.2.Using Chrysidine G as carbon source,potassium ferrocyanide as dopant and PBS as electrolyte,green fluorescent carbon dots(G-CDs)are synthesized by electrolysis at 10 V voltage for fluorescence sensing detection of Cr(Ⅵ).The maximum excitation wavelength of G-CDs is 308 nm,and the emission wavelength is 510 nm.After doping with potassium ferrocyanide,the fluorescence quantum yield is significantly increased to 6.05%and the average particle size of G-CDs is 3-5 nm.The structure and chemical characteristics of G-CDs are characterized by Raman spectroscopy,Fourier infrared spectroscopy and X-ray photoelectron spectroscopy.Experiments showed that Cr(VI)would lead to fluorescence quenching of G-CDs,and the optimal reaction conditions for chromium detection were pH=8.0,incubation temperature at 30℃,and incubation time of 40 min.The fluorescence intensity of G-CDs is linearly correlated with Cr(VI)concentration in the range of 0.25-100 μM,ΔF/F0=0.0186+0.0049CCr(Ⅵ),R2=0.996,LOD=0.15 μM(S/N=3).The detection is not interfered with the presence of other metal ions,which proves that G-CDs has a unique response to Cr(VI).In the detection of drinking water,the recovery rate is 98.8%-100.1%,and RSD is less than 3%.Fluorescence life,Zeta potential test can determine that sensor mechanism is dynamic quenching.3.Using dopamine and epigallocatechin gallate(molar ratio 1:1)as carbon source and PBS as electrolyte,blue fluorescent carbon dots(B-CDs)were obtained by electrolyzing at 10 V voltage and applied to sodium hypochlorite(ClO-)fluorescence sensing.The best excitation wavelength of the carbon dots was 372 nm,the maximum emission wavelength was 462 nm and the average particle size was about 5.5 nm.The structure and chemical properties of B-CDs were characterized by Raman spectroscopy,Fourier infrared spectroscopy and X-ray photoelectron spectroscopy.It is found that ClO-could reduce the fluorescence of B-CDs at 462 nm,and the optimal reaction conditions are determined as pH 8.0,reaction temperature 20℃,and incubation time of 3 min.There is a linear relationship between B-CDs fluorescence and ClOconcentration in the range of 0.5-50 μM,ΔF/F0=0.0056+0.0194CClO-,R2=0.997,LOD=0.2 μM(S/N=3).The sensing method is determined to be dynamic quenching by temperature test and fluorescence life(3.50 ns reduced to 0.65 ns).This method has been successfully applied to detection of ClO-in drinking water,with the recovery between 98.2%-104.3%and RSD less than 3.3%.