The application of magnetic particles in micro-fluidic systems for advanced immunoassays

Magnetic particles (MPs) have been applied to develop fast and miniaturized bioassays because nano/microparticles offer a high surface to volume ratio and enhanced fluid-phase kinetics for biomolecular binding. The magnetic properties of the MPs enable fast and easy magnetic separation of captured analyte. In addition, MPs can be easily manipulated using magnetic fields to generate effective mixing, requiring a smaller amount of antibody with sensitive detection. Mixing and rapid analysis of fluids are important challenges in current microfluidic systems because the interaction between reagents in the fluid is limited by the laminar flow and small diffusivities of relatively large biomolecules.;The investigation described here begins with a sandwich immunoassay using magnetic-luminescent nanoparticles (MLNPs) as carriers in a capillary system for fast analysis. A novel capillary system provides a fast assay time by facilitating reaction. An alternating magnetic field from external electromagnet was applied to enhance mixing for the sample and antibody coated MLNPs. The advantages of the MLNPs-based capillary system included rapid assay time, automated manipulation of the immunoassay and washing, and a reduced reaction volume. Next, superparamagnetic particle dynamics were investigated using competing external magnetic field and viscous drag forces in a capillary tube. Superparamagnetic particles aligned to form chains under stationary conditions in the external magnetic field and the statistics of chain length were investigated by image analysis. The dynamics can be quantified by the dimensionless Mason number and the critical Mason number was determined where the rotation of the capillary prevented the formation particle chains. In the final study, a rapid and simple magnetic particle-based immunoassay has been demonstrated in a rotating capillary mixing system. Antibody-coated micrometer size superparamagnetic particles were used in an assay for rabbit IgG in a sandwich (non-competitive) format. A previously determined critical Mason number was employed as a guide to appropriate experimental conditions of magnetic field strength and rotational speed of the capillary.;The proposed concept of a capillary mixing system for superparamagnetic particles was successfully demonstrated to produce a fast analysis and intensify the capturing of biomolecules. Our experimental investigations lead to a better understanding of superparamagnetic particle dynamics in a rotating flow field to improve the mixing performance in microfluidic systems.