Surface property directed microchannel flows in biosensors

Abstract

It is known that rapid mixing in biosensors is required; however, these sensors may use reagents having small diffusion coefficients and whose mixing time scale is longer than the chemical reaction or molecular event time scale. Thus, it is necessary to overcome the inherent diffusion limited mixing of laminar flow. Many techniques to enhance microfluidic mixing are under development such as slanted wells, shallow grooves, electrokinetic instability mixing and surface layers. In this work, enhanced mixing is explored using lattice Boltzmann simulation techniques of two and three dimensional microfluidic channels at low Reynolds numbers. Surface temperature variations and flow field slip and no-slip boundary conditions emulating hydrophobic and hydrophilic surfaces were applied. The combined effect of wall temperature and surface property distributions presents a new way to manipulate microchannel flow fields. The momentum and thermal lattice Boltzmann equations were coupled via a body force term in the momentum equation. Also, a two dimensional, binary fluid model was incorporated. The results show how various wall temperature distributions, subjected to various velocity wall boundary conditions, can be either beneficial or counter productive to obtain uniform flow temperature profiles in, for example, PCR applications. The addition of the binary fluid model demonstrates the effects of both wall temperature and wall velocity boundary conditions.