Time-series Impedance Detection Method Of Pesticide Residues Based On High-throughput Microfluidic Technology

Pesticide residue detection is an indispensable link in promoting the process of agricultural modernization and promoting the green development of agriculture.The electrochemical biosensor detection method for agricultural residues based on microfluidic technology has the advantages of real-time performance,portability,high accuracy,high throughput detection,high stability and small reagent consumption,which is conducive to promoting the development of the rapid detection platform for agricultural residues to the direction of integration,portability and automation.However,this method still has the following problems:(1)The fabrication process of PDMS microfluidic chips is complex and expensive,most of the chips have low reusability,and paper-based chips also have the disadvantage that it is difficult to control the flow;(2)Curing enzymes or biometric molecules on the surface of the electrode can easily lead to uneven distribution of enzymes,reduced enzyme activity or even denaturation,which will directly affect the detection accuracy of the sensor.In addition,some nanomaterials are usually used in the fabrication of electrodes to improve the sensitivity and specificity of sensors,but these materials are complicated and expensive to fabricate and also need to be cured on the electrode surface.Aiming at the above problems,the subject proposes a sequential impedance detection method based on a high-throughput microfluidic chip.The subject mainly focuses on the design of high-throughput microfluidic detection chips for pesticide residues and the rapid qualitative and quantitative detection methods for pesticide residues.(1)High-throughput microfluidic chips were designed according to the detection requirements of chlorpyrifos,diazinophos and phoxim pesticide residues.The chip mainly consists of two parts: concentration gradient generation chip and paper based microfluidic chemical reaction chip.The concentration gradient generation chip was designed according to the flow and mixing rules of pesticide residue samples in microchannels.COMSOL software was used to optimize channel structure and injection speed parameters to generate pesticide residue samples with concentrations ranging from 0.1 μg/m L to 0.9μg/m L.The enzyme inhibition reaction is integrated into the paper-based microfluidic chemical reaction chip,eliminating the curing step of the enzyme on the electrode.The concentration gradient generation of samples,enzyme inhibition chemical reaction and detection of samples were integrated into the two chips respectively.The PDMS chip could be reused and the chemical reaction process would not be affected.(2)A high-throughput microfluidic chip was combined with a screen-printed electrode to analyze the impedance data of agricultural residue samples in the optimal reaction time of enzyme inhibition,and the impendance-time series was constructed.Feature extraction was carried out for the data in the optimal frequency range,and the feature vector group after dimensionality reduction was obtained.Then the support vector machine classifier was constructed for the feature vector,and the performance of the classifier was tested in the actual spinach sample.The experimental results showed that the classification accuracy of the method used for spinach samples could reach 96.07%,and the qualitative detection of pesticide residues at unknown concentrations could be realized.(3)The equivalent circuit was designed for the electrochemical impedance detection system designed by the project,and the linear fitting of the electronic transfer resistance and concentration data in the circuit was carried out to build a regression model to achieve the quantitative detection of pesticide residues.After that,the method repeatability and recovery of three pesticide linear regression models were tested.The results showed that the recoveries of the three pesticides ranged from 94.8% to 112.2%,and the relative standard deviations were within 7.5%.In conclusion,impedance time series rapid detection of pesticide residues based on the high-throughput microfluidic chip in this study can achieve qualitative and quantitative detection of pesticide residues.