| Impedance biosensors are promising for applications in the field of food safety, because of their advantages such as rapid detection, label-free assay. However the commercial instruments for impedance biosensors have common shortages, such as large size, high cost and complex operations, which have limited the development of impedance biosensors.In this study, a portable interdigitated microelectrode based impedance biosensor instrument was studied for rapid detection of pesticide residue and foodborne pathogen. After research, an equivalent circuit and optimized detection frequencies for portable instrument were determined. It was proof that the instrument could replace the commercial instrument through multi-target evaluation. This instrument will provide as a useful tool for in-situ detection of food safety. The main contents and results of this research are summarized as the follows:(1) An interdigitated microelectrode based impedance biosensor was developed for the detection of pesticide residue. Based on the additive assay method, the calibration curve for detection of chlorpyrifos was established. The optimized detection frequencies and an equivalent circuit for detection of pesticide residue were studied. The relationship between electron transfer resistance and measured impedance magnitude was innovatively studied, and indicates obvious linear relationship under specific frequencies. It provides a better way to detect target concentration by measuring the impedance magnitude directly.(2) A portable impedance biosensor instrument system was constructed; include a portable instrument, a micro-printer and computer application software. This instrument could measure impedance under multiple exciting frequencies and voltages. It will be conducive to avoid the shortages of commercial instruments for impedance biosensors.(3) Calibration devices with quick connect function for the impedance biosensor was investigated. It is a convenient and useful tool to calibrate the developed impedance instrument. An equivalent circuit for the calibration device was studied, and the relationship between nominal resistance and parasitic parameters (inductance and capacity) were developed. It is proved that the calibration devices work well for the instrument impedance calibration.(4) The portable biosensor instrument was evaluated synthetically by detecting three different kinds of targets. By detecting the commercial standard calibration module, the results demonstrated that the maximum relative impedance magnitude error of the instrument is 1.21% and the maximum phase difference is 0.670°. After investigating the impedance stability of three typical buffer solutions, it was illustrated that the impedance value of buffer solutions in the microfluidic chip had a downtrend, but trend to be stable while measurement times increased. The instrument was also evaluated to measure two buffer solutions, KPL wash solution and manitol solution, when they became stabilized. Under three frequencies which same to the commercial instrument (1 kHz,10 kHz and 100 kHz), the maximum relative impedance magnitude error for buffer solutions is 4.60% and the maximum coefficient of variation of eight measurements is 0.94%. Because the research anti-chlorpyrifos antibody was used up before the evaluation step, the instrument was only evaluated to detect E.coli O157:H7 as target bacteria after immumomagnetic separation. Under four working frequencies, the maximum relative impedance magnitude error is 2.91% and the maximum phase difference is 1.892°, at the working frequency of 100 kHz. The instrument detection time is less than 5 seconds. The instrument features rapid detection speed and high measurement precision, which can be used to replace the commercial impedance measurement instrument. The results showed that the impedance biosensor instrument was developed successfully for applications in food safety. |
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