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Jiang X.,Nanjing Forestry University | Jiang X.,Haitong Food Science and Technology Company Ltd | Wang W.,Haitong Food Science and Technology Company Ltd | Lu L.,Haitong Food Science and Technology Company Ltd | And 3 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2014

The objective of this study was to develop a label free electrochemical immunosensor for detection of pesticide chlorpyrifos (CPF) in agricultural products. The surface modification of sensors consisted of three successive steps: 1) surface cleaning; 2) increasing the surface coverage of hydroxyl groups; 3) silanization. The CPF hapten conjugate used as recognizing elements were immobilized on the surface of an electrode. Cyclic votammetry was investigated before and after hapten coating, which that confirmed CPF hapten could be successfully coated on the electrodes. The spiked CPF solution was diluted into various folds and mixed with an CPF antibody solution. The detection method was based on an indirect competitive reaction of a limited anti-CPF polyclonal antibody in a sample solution with immobilized hapten, and with a pesticide analyte in the sample solution. The antibody-antigen affinity interactions were investigated by impedance spectroscopy and quartz crystal microbalance. Impedance measurements were performed using a three-electrode setup, which consisted of a gold electrode as a working electrode, a platinum auxiliary electrode, and an Ag/AgCl reference electrode. For impedance measurement, a sine-modulated AC potential with an amplitude of 5 mV was applied to the modified electrodes. The Faradic impedance spectra were recorded in the frequency range from 1 Hz to 100 kHz, respectively. The semi-circle diameter in the Nyquist plot represented the electron-transfer resistance in an equivalent circuit, decreased with increasing analyte concentrations. For the QCM test, a crystal electrode was mounted in the base of a cylindrical test cell using an "O-ring". One face of the crystal was exposed to the test liquid, while the other was exposed to air. After the antigen modified chips were reacted with the mixture, the variations between the initial and final resonance frequency in PBS was recorded. The signal response of the biosensing system to pesticide CPF concentrations was linear, with the range tested from 0.01-10 μg/mL, with the correlation coefficient of 0.98. The result indicated that EIS was capable of monitoring the change in electron-transfer resistance resulting from anti-CPF antibody-antigen interaction. QCM was also the ideal tool for probing antigen-antibody molecular recognition. The immunosensor can be suited to the detection of pesticide residues in agricultural products, such as Chinese green vegetables and apples. The immunosensor was shown to be sensitive, accurate, rapid, and economical, thus providing a viable alternative to current pesticide detection methods. The systems can be used to determine pesticide CPF down to 0.01 μg/mL. The recovery rate was more than 85 percent. The total detection time was less than 1 h. The mean within-assay variability of detected results was less than 5 percent. It can be used repeatedly after sensor generation.

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