Three Dimensional Gold Nanoelectrode Ensembles And Its Application In AFB₁Immunosensor

In this thesis, the research status and progress on nanoelectrode ensembles and electrochemical biosensing for aflatoxins in the world were reviewed. Three dimensional nonoelectrode ensembles (3DNEEs) was prepared and characterized, and a model was built to simulate the electrode process and kinetics parameters on ordered3DNEEs. A label-free impedimetric immunosensor with high sensitivity for AFB1was fabricated based on poly(o-phenylenediamine)(PoPD) modified3DNEEs (PoPD/3DNEEs).The conditions for chemical deposition of gold on polycarbonate filter membrane were optimized. The morphologies and compositions of3DNEEs were evaluated by SEM, EDX, and XRD.3DNEEs was proved to be pure gold and the nanowires were vertically oriented in parallel. Electrochemical characterization was performed in H2SO4and K3Fe(CN)6/K4Fe(CN)6.3DNEEs possessed larger real surface area than geometric area. The diffusion domain on3DNEEs was heavily overlapped, and linear diffusion dominated the diffusion process, while radial diffusion shared “a cup of rich soup”.The model of ordered3DNEEs was built with Comsol Multiphysics4.4multiphysics simulation software and cyclic voltammograms and impendence spectra on3DNEEs with various radius, length, and spacing were systematically simulated for the first time. Simulation results of cyclic voltammograms indicated that there existed a critical spacing dmin on3DNEEs and only3DNEEs with a spacing wider than dmin could get the S shape cyclic voltammograms at some scan rates. dmin was found in linear correlation with surface area or diameter of the nanaowire, along with the variation of the length of the nanowire from200nm to600nm on fixed diameter of100nm or the diameter of the nanowire from50nm to400nm on fixed length-diameter ratio of3:1. Active area of the electrode, electron transfer impedance, apparent reaction rate constant and other parameters were calculated by the simulation and fitting of the impedance spectra. Calculated results coincided with parameters set for simulation. A segment of circular arc was observed in the spectra on3DNEEs at low frequencies, which indicated the influence of barrier diffusion on the diffusion process at nanowires.PoPD/3DNEEs with ladder-like and PAN-like structures was prepared respectively in this thesis, and stability in solutions involved in fabrication and detection of the immunosensor was evaluated. Ladder-like PoPD/3DNEEs indicated better stability. Electrochemical immunosensor for AFB1based on PoPD/3DNEEs was fabricated for the first time. Optimization was performed for polymerization conditions, and time for crosslinking and BSA blocking in the fabrication of molecular recognition membrane, as well as detection system, pH value, and time for incubation with antigen of the sensor. The model of the molecular recognition membrane was established and equivalent circuit was built to simulate impedance spectra. The immunosensor for AFB1fabricated in this thesis was proved to possess wide detection range between3.0×10-9~1.0×10-7g/mL and low detection limit of1.5×10-9g/mL, which was lower than limitation standards set by EU. The immunosensor was superior to the work of other researchers on labelless impedimetric immmunosensor for AFB1.