Enhanced Microfluidic Sample Homogeneity and Improved Antibody-Based Assay Kinetics Due to Magnetic Mixing.

Recent global events have distinctly demonstrated the need for fast diagnostic analysis of targets in a liquid sample. However, microfluidic lab-on-a-chip devices for point-of-care diagnostics can suffer from slow analysis due to poor mixing. Here, we experimentally explore the mixing effect within a microfluidic chamber, as obtained from superparamagnetic beads exposed to an out-of-plane (vertical) rotating magnetic field. Various magnetic protocols are explored, and the level of sample homogeneity is measured by determining the mixing efficiency index. In particular, we introduce a method to induce effective mixing in a microfluidic chamber by the actuation of the same beads to perform global swarming behavior, a collective motion of a large number of individual entities often seen in nature. The microparticle swarming induces high fluid velocities in initially stagnant fluids, and it can be externally controlled. The method is pilot-tested using a point-of-care test featuring a bioluminescent assay for the detection of antibodies. The mixing by the magnetic beads leads to increased assay kinetics, which indeed reduces the time to sensor readout substantially. Magnetic microparticle swarming is expected to be beneficial for a wide variety of point-of-care devices, where fast homogeneity of reagents does play a role.