| With the long term use of pesticides in agricultural products and environment, excessive pesticide residues has caused considerable hazard on ecological environment and health of human. So pesticide residues in food have been paid more attention over the world. Now, People would pay growing awareness of food and environment safety, since it’s extremely urgent to strengthen the detection of pesticide residues. Some instrumental methods have been used to detect pesticides, such as gas chromatography (GC), liquid chromatography (LC), Immunosorbent assay, gas chromatogram mass spectrometer(GC-MS) and liquid chromatogram mass spectrometer (LC-MS) offer high sensitivity and specificity and have the potential for simultaneous determination of multiple analogues, the associated high costs and time-consuming labor requirements are necessary. Searching for a new, simple, low-cost, portable, and sensitive analytical method is of considerable interest.Photoelectrochemical measurement is a newly developed technique for the sensing platform, which is based on the electron transfer among analyte, semiconductor, and electrode with photoirradiation. Coupling photoirradiation with electrochemical detection, photoelectrochemical sensors have the advantages of both optical methods and electrochemical sensors. Thus, this technique has attracted considerable interests as a newly developed and promising analytical technique. Moreover, the utilization of electronic detection makes the photoelectrochemical instruments simpler and low-cost compared with those of the conventional optical methods. Many kinds of pesticides have not electroactive performance or are weak electroactive, may be analyzed by their photoelectrochemical effect. This paper aims mainly are to explore simple, sensitive and rapid photoelectrochemical methods that can detect nonelectroactive or weak electroactive pesticides such as amide pesticides of acetochlor, cyclohexanedione clethodim, neonicotinoid pesticides acetamiprid. Specific contents and results are as follows:1. A derivative photoelectrochemical sensing platform for herbicide acetochlor based on TiO2-poly (3-hexylthiophene)-ionic liquidnanocomposite film modified electrodesNonelectroactive acetochlor can be indirectly determined through the photocatalytical degradation of acetochlor. A derivative visible light photoelectrochemical sensor for indirect detection of the herbicide acetochlor using TiO2-poly(3-hexylthiophene)-ionic liquid nanocomposite is constructed. Poly (3-hexylthiophene) (P3HT) was synthesized via chemical oxidative polymerization with anhydrous FeCl3 as oxidant,3-hexylthiophene as monomer, chloroform as solvent, and the functional TiO2 nanoparticles were facilely prepared by blending TiO2 nanoparticles and P3HT in the ionic liquid 1-Butyl-3-methylimidazolium hexafluorophosphate solution at room temperature. Operational parameters, including the photolysis time, ratios of TiO2 to P3HT, bias voltage and pH of buffer solution have been optimized. Under optimal conditions, the proposed photoelectrochemical method could detect acetochlor ranging from 0.5 to 20 μmol L-1 with a detection limit of 0.2 nmol L-1 at a signal-to-noise ratio of 3. The assay results of acetochlor in water samples with the proposed method were in acceptable agreement with those of the gas chromatograph-mass spectrometer (GC-MS) method. The promising sensor opens a new opportunity for fast, portable, and sensitive analysis of acetochlor in environmental samples.2. Photoelectrochemical detection of the herbicide clethodim by using amino-MIL-125(Ti)/Ti02We describe a highly sensitive photoelectrochemical sensor for the herbicide clethodim that works at zero electrochemical potential (versus a saturated calomel electrode). It was constructed using amino-MIL-125/TiO2 (MIL stands for Materials from Institute Lavoisier), an amine-functionalized metal-organic framework (MOF) modified with TiO2. It was synthesized by a one-step solvothermal method and placed on a glassy carbon electrode where it displays photoelectrocatalytic activity. The amino-MIL-125/TiO2 was characterized by scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy and X-ray diffractometry (XRD). In a sensing process, amino-MIL-125 was excited by visble light irradiation to produce electrons. These excited electrons were delievred into the illuminated TiO2 and then to the glassy carbon electrode. Simultaneously, positive charged holes (h+) of TiO2 may form and migrate to the amino-MIL-125 MOF, which can react with H2O to generate·OH, and then it converts clethodim into clethodim· that promoted the amplifying photocurrent response. This photoelectrochemical method enables clethodim to be quantified in the 0.2 to 25 μmol L-1 concentration ranging, with a 10 nmol L-1 detection limit (at a signal-to-noise ratio of 3). The assay was applied to determine clethodim in soil samples, and results were in acceptable agreement with data obtained by liquid chromatography/mass spectrometry (LC/MS).3. Visible-light-activated NH2-MIL-125(Ti)/TiO2 photoelectrochemical biosensor for the detection of pesticide acetochlor based on its inhibition towards glucose oxidaseA highly sensitive and selective photoelectrochemical (PEC) method for the detection of acetochlor has been developed based on a glucose oxidase (GOx) biosensor in this work. NH2-MIL-125(Ti)/TiO2 nanocomposite, as a new functional material, was used for the immobilization of GOx by using chitosan as the dispersion matrix. Under visible light irradiation, the GOx/CS/NH2-MIL-125(Ti)/TiO2 nanocomposite can generate a stable photocurrent in the glucose solution. After introducing acetochlor into the glucose containing phosphate buffer solution, the activity of GOx was inhibited thus caused the drop of the photocurrent. Under the optimal experimental conditions, the inhibition of the photocurrent was proportional to the concentration of acetochlor in the range of 0.02-1.0 nmol L-1and 10-200 nmol L-1 with the detection limit of 0.003 nmol L-1 (S/N=3). The resulting biosensor was further evaluated by monitoring acetochlor. in spiked fruit and vegetable samples, showing fine applicability for the detection of acetochlor in real samples.4. A novel sensor for the detection of acetamiprid in vegetables based on its TiO2 photocatalytic degradation compoundAn electrochemical method for the indirect determination of acetamiprid was studied, using titanium dioxide photocatalysts coupled with a carbon paste electrode. The cyclic voltammetric results indicated that the photocatalytic degradation compound of acetamiprid had electroactivity in neutral solutions. The amount of acetamiprid was further indirectly determined by differential pulse anodic stripping voltammetric analysis as a sensitive detection scheme. The experimental parameters were optimized with regard to the photocatalytic degradation time, pH of buffer solution, accumulation potential and accumulation time. Under optimal conditions, the proposed electrochemical method could detect acetamiprid concentrations ranging from 0.01-2.0 μmol L-1, with a detection limit (3 S/N) of 0.2 nmol L-1. Moreover, the proposed method displays excellent selectivity, good reproducibility, and acceptable operational stability and can be successfully applied to acetamiprid determination in vegetable samples with satisfying results.
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