Numerical analysis of transport and binding of a target analyte and functionalized magnetic microspheres in a microfluidic immunoassay

In situ binding of a target analyte on functionalized magnetic microspheres in a straight microchannel, representing a microfluidic immunoassay, is investigated numerically using an Eulerian-Lagrangian approach. Magnetic particles in the microfluidic channel are transported, using an externally imposed magnetic field, in such a manner that the particle-analyte collision is facilitated. The effects of both-ways momentum coupling between the dispersed and fluid phases on the fluid flow, particle trajectories and the analyte concentration profiles have been investigated. The particle-analyte collision is assumed to result in chemical binding between the analyte and the functionalized magnetic particles. Analyte concentration and fluid velocity fields are found to be influenced by dipole strength (P) and particle loading. In situ target analyte binding on magnetic microspheres has been quantified in terms of binding efficiency (BE), which is found to be functions of the particle loading, particle radius, dipole strength, flow velocity and the fluid viscosity. While particle loading increases, the BE also increases, but the analyte binding per particle slightly decreases. With increase in dipole strength, the BE first increases and then decreases. If the particle loading is increased, the maximum BE occurs at a higher value of P, but at a lower value of viscosity. An increase in flow velocity is found to have strong adverse effect on the BE. The study is important for the selection of optimum operating parameters so that the analyte BE of a magnetic particle-based immunoassay can be maximized.