Mass transport and surface reactions in microfluidic systems

We provide analysis of different regimes of diffusion and laminar flow convection combined with bimolecular surface reactions relevant to biochemical assays performed in microfluidic devices. Analytic solutions for concentration fields are compared to predictions from two-dimensional finite element simulations for the various operation regimes. The analytic and numerical results extend the transport models beyond the models commonly used to interpret results from surface plasmon resonance (SPR) experiments. Particular emphasis is placed on the characterization of transport in shallow microfluidic channels in which the fully developed transport regime dominates rather than the mass transfer boundary layer transport typically encountered in SPR. Under fast reaction and diffusion conditions, the surfaces saturate following moving front kinetics similar to that observed in chromatographic columns. Two key parameters relevant to on-chip biochemical assays and microfluidic sensors are studied and compiled: the capture fraction of the bulk analyte at the surface and the saturation time scale of the reactive surfaces. The physical processes in the different regimes are illustrated with data from the relevant microfluidics literature. (c) 2005 Elsevier Ltd. All rights reserved.