A Lable-free Impedimetric Electrochemical DNA Senor For AFB₁ Based On Gold Electrode

Electrochemical DNA biosensors provides a new opportunity for AFB₁ detection because of the advantages of time-saving,label-free measurement and high sensitivity.However,in the reported literatures on the AFB₁ electrochemical DNA biosensors,there are still some problems such as less quantitation of DNA,complicated preparation process and poor sensitivity.This could be ascribed to the improper DNA immobilization method,poor electrode property and specificity.Therefore,in this thesis the thiolated ss DNA?HS-ss DNA?was directly immobilized on the surface of electrodes through DNA self-assembling to achieve the purpose of simplification;The DNA sequence that specific to AFB₁ was studied for the first time.The PoPD modified electrodes?PoPD/MGE?and three dimensional nonoelectrode ensembles?3DNEEs?were used as base electrodes and more active groups of PoPD electropolymerization and large surface of the 3DNEEs provided a larger active sites for DNA immobilization.The HS-ss DNA was directly assembled on the surface of MGE through the strong chemical bond Au-S.The DNA senor of DNA/MCH/MGE was constructed and the preparation process is simpler and more efficient.Optimizations were performed for parameters in the fabrication process of DNA senor,as well as detection system.AFB₁ concentrations were detected by electrochemical impedance spectroscopy?EIS?.The equivalent circuit was built by analyzing the interface composition of the sensor to simulate impedance spectra.The detection limit was 2.1×10-10 g·m L-1?S/N=3?with a linear AFB₁ concentration range of 5.0×10-10².0×10-8 g/m L.In this paper,the DNA sequence that specific to AFB₁ was optimized for the first time.The DNA senor was constructed by using the optimized DNA and the detection limit was 2.3×10-12 g/m L?S/N=3?.Selectivity measurement showed that the DNA sensor constructed in this thesis had highly selective detection for AFB₁.The cyclic voltammetry was used for PoPD electropolymerization on MGE.The DNA was immobilized on the PoPD/MGE by glutaraldehyde cross-linking and the DNA senor of DNA/GA/PoPD/MGE was constructed.A wide concentration range of AFB₁ was investigated by the EIS method.The sensor exhibited a linear range from 5.0×10-12¹.0×10-8 g/m L with a detection limit of 2.3×10-12 g/m L.It can be seen that the sensitivity of the sensor was improved by using PoPD electropolymerization.3DNEEs were fabricated by template synthesis.Scanning electron microscopy?SEM?and Energy Dispersive X-ray Detector?EDX?were used to characterize the morphology and composition of 3DNEEs.3DNEEs was confirmed not only parallel orientation and regular arrangement,but also high purity.An impedimetric DNA sensor for AFB₁ detection was fabricated based on gold 3DNEEs modified with thiolated ss DNA.The quantitation of DNA immobilized on the 3DNEEs was calculated.The result showed that the surface density of DNA assembled on the 3DNEEs was about one order of magnitude higher than that on the MGE.A wide concentration range of AFB₁ was investigated by the EIS method.The detection limit was 8.0×10-13 g/m L?S/N=3?with a linear AFB₁ concentration range of 1.0×10-12¹.0×10-8 g/m L.The preparation process of the senor was simple and efficient.The special three dimensional structure and large surface of the 3DNEEs provided a larger active area for DNA assembly.The performance was superior to the work of other researchers on label-free impedimetric electrochemical DNA sensor for AFB₁.The DNA sensor was used to detect AFB₁ concentrations in corn samples,and the average recovery was 102.6%.