Analysis of reaction-transport phenomena in a microfluidic system for the detection of IgG

A spatially two-dimensional mathematical model of microfluidic biosensor for immunological determination of human immunoglobulin G (IgG) with the use of Protein A (PA) immobilized on the internal walls of a microchannel is presented. Convection flow in the microdevice is induced by an imposed difference of electric potential (electroosmosis). In the model, the electroosmotic convection is described using the slip boundary conditions that can be defined by the Helmholtz-Smoluchowski equation. Incubation phase (formation of the immobile PA-IgG complex) of the immunoassay has been studied. Effects of the antibody concentration in a sample, the imposed difference of electric potential, the surface heterogeneities in the reaction zone, and other model parameters on the saturation time were determined. It was found that the surface heterogeneities could form complex velocity fields at the location of the adsorption zone: either an intensive flow at the microchannel walls or the nozzle-like flow. Generally, the local acceleration of the flow causes the decrease of the mass-transfer resistance. Further, imposed electric field of a proper orientation was able to shorten the incubation phase to 600 s, assuming the microchannel device with the diameter of 100 mu m and the chosen reaction kinetics. Hence, the incubation phase could be substantially reduced enabling, e.g., fast diagnostics. Simulation of the effects of the antibody sample concentration revealed good qualitative agreement with experimental data obtained in a similar microfluidic device.