Physics of magnetic particle actuation for rapid biosensing

Magnetic particles are widely used in biosensing systems, but the applied magnetic actuation is mostly of a static nature. Here, we study and develop novel dynamic actuation principles, based on time-dependent magnetic fields and field gradients. Ensembles of magnetic particles show surprising behaviors in dynamic fields, originating from magnetic and hydrodynamic interactions between particles, fluid and surfaces. For example, chains of particles can be rotated and repeatedly broken and reformed, inducing chaotic fluid flow and improving the capture of molecules from the fluid. Particle-based molecular capture is studied by quantifying the roles of diffusion and chemical association. Furthermore, we describe mechanisms to redistribute and transport particles over a surface with high velocity. Finally, we discuss how the particle actuation methodologies can be integrated and concatenated in order to realize biosensing systems that are entirely controlled by magnetic fields.