Particle concentration and separation using magnets

A variety of wearable magnetic assemblies are provided that are configured to produce magnetic fields having high field magnitudes and/or high field gradients. These wearable magnetic assemblies are configured to exert forces on magnetic particles disposed in a portion of subsurface vasculature (e.g., a portion of the ulnar artery near the wrist) proximate to the magnetic assemblies. These magnetic assemblies include a plurality of dipolar permanent magnets. The forces can act to attract, slow, speed, separate, or otherwise influence the magnetic particles in various applications. In some embodiments, the magnetic particles are configured to bind to an analyte of interest. The collection, separation, and/or concentration of the magnetic particles can enable detection of one or more properties of the analyte, modification of the analyte, and/or extraction of the analyte bound to the magnetic particles.