Performance analysis of a Si-NW biosensor for detection of charged biomolecules

Biosensors based on Si-NW have already demonstrated for the detection of DNA, proteins, pH levels, etc. Although it is generally accepted that Si-NWs with lower doping density and smaller diameter provides better sensitivity, the influence of factors like surrounding environment (air/water) and electrostatic screening due to the ions in the 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 predict the trade-off between average response time and minimum detectable concentration. Investigating the average response time this study shows that, Si-NW sensor gives faster response than that of nanoscale ISFET sensor. Also the PoissonBoltzmann equation is solved numerically and 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. This study concludes that, the parameters such as the dimension of the Si-NW, the doping level of the Si-NW, the ions concentration in the solvent, pH of the solution etc that limit the performance of a Si-NW sensor must be optimized for high sensitivity biomolecule detection. Numerical simulation is carried out using biosensorLAB tool, a simulator from Nanohub.org, which is an online based java platform engine.