Rapid Detection Of Hg²⁺ And Organophosphorus Pesticides In Fruit Juices Based On Carbon Dots And Fluorescent Technique

Hg and pesticide pollution are the important factors which can affect food safety. The heavy metals pollution is multi-original, hidden and accumulated, and has become one of the major global environment problems. Hg in the body is accumulated, and have a long half-life, and can produce acute and chronic toxicity reaction, and also has teratogenic, carcinogenic and mutagenic effects. Organophosphorus compounds are one of major factors of acute pesticide poisoning, and significant detection objects of the pesticide residues in fruits and vegetables. Organophosphorus compounds can also cause chronic poisoning. Long-term exposure to pesticide residues can make the pesticides constantly accumulate in the body, which can cause physiological disorder, affect the reproductive system, and cause fetal abnormalities. A number of pesticides have teratogenic, carcinogenic and mutagenic effects. With increasing of the health and the environmental protection consciousness, Hg and pesticide residues analysis research has attracted tremendous attention.Owing to high sensitivity, low-cost, and operational simplicity and rapidity, fluorescent detection have attracted tremendous attention. In this paper, one kind of Hg(Ⅱ) ion sensor and two kinds of OPs sensors were fabricated based on carbon dots. The main contents could be divided into three aspects as follows:(1) One of kind nitrogen-dopped carbon dots were prepared with hair, and one kind of sensor for Hg2+ ion was constructed based on the charge transfer beteewn carbon dots and Hg2+ ion. The preparation was completed by simple hydrothermal methods withouot any additive. The N-CDs were characterized by transmission electron microscopy, high-resolution transmission electron microscopy, infrared spectroscopy, X-ray photoelectric spectroscopy, UV-vis absorption spectrum and fluorescence spectrum. These results showed that the surface of the carbon dots were rich in hydroxyl and carboxyl hydrophilic group, so the carbon dots were very stable in water. The fluorescence quantum yield was up to 24.8%. Under the optimal conditions, the fluorescence quenching efficiency was proportional to the concentration of Hg2+ ion in the range 0.002-0.02 mg/kg. The detection limit(S/N = 3) was 0.0007 mg/kg, which was below the maximum residue limit of the fruit juices of our country entry-exit inspection(SN/T06-2007,0.01 mg/kg). Hg2+ ion in fruit juice samples was determined by standard addition method, the average recoveries were between 103% and 104%, and RSDs were between 3.5% to 4.9%. The recoveries and RSDs is close to that of GB/T 5009.17 2003, the detection speed was rapid and the detection limit was slightly higher. In addition, the testing object of this method was Hg2+ ion, the testing object of the GB/T 5009.17 2003 was the total content of mercury.(2) One kind of the rapid screening method for organophosphorus compouds in fruit juices was first constructed based on the inhibition of acetylcholinesterase. These carbon dots were obtained by simple hydrothermal reaction using feather as carbon resource. The fluorescence of these carbon dots can be selectively quenched by Cu2+ ion. When acetylcholinesterase and acetylthiocholine were introduced into the system, thiocholine came into being, which can react with Cu2+ ion, and restored the fluorescence of the system. However, when dichlorvos was introduced, the activity of AChE was inhibited, which can quench the fluorescence of the above system.These CDs were characterized by transmission electron microscopy, high-resolution transmission electron microscopy, infrared spectroscopy, X-ray photoelectric spectroscopy, UV-vis absorption spectrum and fluorescence spectrum. These results showed that the surface of the carbon dots were rich in hydroxyl and carboxyl hydrophilic group, so the carbon dots were very stable in water. The fluorescence quantum yield was up to 11.6%. Under the optimal conditions, the enzyme inhibition rate was proportional to the logarithm of the dichlorvos concentration in the range 0.0013-0.088 mg/kg. The detection limit(S/N = 3) was 8.4 x 10-4 mg/kg, which was much lower than the maximum residue limits(MRLs) as reported in the European Union pesticides database as well as those from the U.S. Department Agriculture(0.01 mg/kg). Dichlorvos in fruit juice samples was determined by standard addition method, the average recoveries were between 94% and 104%, and RSDs were between 4.5% to 6.3%. The recoveries and RSDs is close to that of GBT 19649-2006, the detection speed was rapid and the detection limit was lower. In addition, the testing object of this method was the total content of pesticides, the testing object of GBT 19649-2006 was specific pesticide.(3) One kind of the rapid screening method for organophosphorus compouds in fruit juices was first constructed based on the inhibition of tyrosinase. These carbon dots were obtained by simple hydrothermal reaction using citric acid as carbon resource and L-tyrosine methyl ester as modification reagent. These carbon dots were characterized by transmission electron microscope, high resolution transmission electron microscopy, X-ray diffraction spectrum, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. These results showed that the surface of the carbon dots were modified by L-tyrosine methyl ester and the aim of this experiment was completed. Tyrosinase can catalyze the oxidation of tyrosine methyl ester on the surface of carbon dots to corresponding quinone products, which can quench the fluorescence of carbon dots. When organophosphorus pesticides were introduced in system, they can decrease the enzyme activity, thus decrease the fluorescence quenching rate, Based on the above principle, the organophosphorus pesticide sensor was constructed. The modification and formation of carbon dots was completed by one step reaction. Experimental results showed that the enzyme inhibition rate was proportional to the logarithm of the methyl parathion concentration in the range 0.000026 – 26 mg/kg. The detection limit(S/N = 3) was 1.3 × 10-5 mg/kg, which was much lower than the maximum residue limits(MRLs) as reported in the European Union pesticides database as well as those from the U.S. Department Agriculture(0.01 mg/kg). Methyl parathion in fruit juice samples was determined by standard addition method, the average recoveries were between 98% and 106%, and RSDs were between 2.4% to 5.4%. The recoveries and RSDs is close to that of GBT 19649-2006, the detection speed was rapid and the detection limit was lower. In addition, the testing object of this method was the total content of pesticides, the testing object of GBT 19649-2006 was specific pesticide.