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 5mV was applied to the modified electrodes. The Faradic impedance spectra were recorded in the frequency range from 1Hz 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 0.01-10μg/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 0.01μg/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.%研究了一种无标记的电化学免疫传感器，用于农产品中的毒死蜱农药残留的快速检测。将毒死蜱人工抗原作为生物识别元件固定在金电极的表面，采用间接竞争法原理，样品中的被测组分与电极上的固定化包被抗原竞争性结合溶液中的抗体。抗体抗原结合反应通过电化学阻抗谱和石英晶体微天平进行表征。将该免疫传感器用于检测青菜、苹果等农产品中的毒死蜱农药残留。结果表明，此免疫传感器灵敏度好、准确度高；对毒死蜱农药的检测限为0.01μg/mL，回收率大于85%，检测时间小于1 h，变异系数小于5%，传感器经过再生处理后能重复使用，经济性较好。该研究可为实现快速检测农产品中农药残留传感器的商品化提供参考。
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