Pore Geometry Optimization of Nanocrystalline Silicon Oxide Impedance Biosensor

Nanocrystalline silicon oxide impedance biosensor has a promising feature of displaying a concentration dependent resonant peak in the sensitivity characteristics, which introduces an electrical marker for selectivity. However, the design of optimum pore geometry for a desirable combination of sensitivity, selectivity, and repeatability is expected to be non-trivial due to the effect of electrical double layer impedance at the electrode-electrolyte interface and local charge modulation at the interface of the cylindrical and the hemispherical regions owing to the mutual interference of the electric field lines. In this paper, the detailed theoretical and experimental investigations of the effect of pore geometry on the sensing performance have been reported. The pore impedance in the transmission line model of such sensors has been evaluated by solving the Poisson Nernst Planck equation using the finite-element method. Aflatoxin B1 (AFB1) and Ochratoxin A (OTA) have been used as the specific and non-specific antigen, respectively. It has been observed that the sensitivity and selectivity parameters along with their repeatability index change oppositely and hence the maximum figure of merit does not vary in accordance with the aspect ratio of the pores. Furthermore, the optimized dimensions have experimentally resulted in tripling of the figure of merit compared with the unoptimized dimension reported in the previous literature. This effect has led to enhancement in accuracy of detection by more than an order of magnitude and selectivity by two orders of magnitude.