Systematic Optimization for the Design of Si-NW Biosensor

Abstract

Biomolecular analysis at very low concentrations is becoming increasingly important. Semiconducting nanowires have been reported as highly sensitive biosensors. Biosensor based on Si-NW has already demonstrated ultrasensitive detection of DNA, proteins, pH levels, etc. Although it is generally accepted that NWs with lower doping density and smaller diameter provides better sensitivity, the influence of factors like electrostatic screening due to the ions in the solution, analyte concentration, pH of the electrolyte solution on NW sensor performance needs to be explained for the systematic optimization of sensor design. In this theoretical study a simple analytical model, based on reaction-diffusion theory is developed to obtain the minimum detectable concentration by a Si-NW biosensor. Investigating the average response time this study shows that, for a reasonable incubation time (500 sec), Si-NW sensor can detect down to about 350 fM concentrations. Also the Poisson Boltzmann Equation is solved analytically based on the result of the diffusion-capture model to show that the electrostatic screening within an ionic environment limits the response of a Si-NW biosensor. In this research work, maximum pH sensitivity achieved for Si-NW sensor is 45 mV/pH. This study concludes that, the parameters such as the dimension of the Si-NW, the doping level of the Si-NW, analyte concentration, the ions concentration in the solvent, pH of the solution etc must be optimized for high sensitivity biomolecule detection.