Numerical investigation of flow-through immunoassay in a microchannel

Immunomagnetic separation (IMS) is a method to isolate biomaterials from a host fluid in which specifically selected antibodies attached to magnetic particles bind with their corresponding antigens on the surface of the target biological entities. A magnet separates these entities from the fluid through magnetophoresis. The method has promising applications in microscale biosensors. We develop a comprehensive model to characterize the interaction between target species and magnetic particles in microfluidic channels. The mechanics of the separation of target nonmagnetic $N$ particles by magnetic $M$ particles are investigated using a particle dynamics simulation. We consider both interparticle magnetic interactions and the binding of the functionalizing strands of complementary particles. The temporal growth of a particle aggregate and the relative concentrations of $M$ and $N$ particles are investigated under different operating conditions. A particle aggregate first grows and then exhibits periodic washaway about a quasisteady mean size. The washaway frequency and amplitude depend on the initial fractional concentration of $N$ particles while the aggregate size scales linearly with the dipole strength and inversely with the fluid flow rate.