Numerical characterization and optimization of the microfluidics for nanowire biosensors.

The present study aims to enhance the analyte transport to the surface of nanowires (NWs) through optimizing the sensing configuration and the flow patterns inside the microfluidic channel, and hence to reduce the response time of NW biosensors. Specifically, numerical simulations were carried out to quantitatively investigate the effects of the fundamental surface reaction, convection, and diffusion processes on the sensing performance. Although speeding up all these processes will reduce the sensing response time, enhancing the diffusional transport was found to be most effective. Moreover, the response time of NW biosensors is inversely proportional to the local concentration of the analyte in the vicinity of the NWs, which suggests that the sensing response time can be significantly reduced by replenishing the local analyte rapidly. Therefore, the following three optimization strategies were proposed and their effects on the time response of NWs were characterized systematically: device substrate passivation, microfluidic channel modification, and suspending NWs. The combination of these three optimization methods was demonstrated to be able to reduce the response time of NW biosensors by more than 1 order of magnitude.