High-Magnetization Silicone Microbeads with Low Autofluorescence for Biotech Applications

Abstract

High-magnetization silicone microbeads with low autofluorescence for biotech applicationsMagnetic microbeads are used in a wide variety of applications within the biophysics community, including magnetic separations, microscale force spectroscopy, and immunological assays. In addition, they show promise in targeted hyperthermia and drug delivery applications, such as in the treatment of cancerous tumors. For most purposes, a high magnetic content is of primary importance.We present here a bottom-up approach for fabricating magnetic beads that allows for large magnetic forces which scale linearly with bead volume. We begin with a high concentration magnetic-nanoparticle / silicone-polymer composite containing as much as 50% wt. nanoparticles, which is subsequently formed into beads via an emulsion polymerization process. The resulting magnetic beads are uniformly saturated with magnetic content throughout their volume. In addition, our beads exhibit minimal autofluorescence relative to polystyrene spheres.To measure magnetic forces, we pulled magnetic beads of varying diameter through a viscous fluid using a fixed magnetic field geometry. Calculations of Stokes drag obtained via video tracking software allowed us to determine applied magnetic forces on each bead. Our data show that magnetic forces on our microbeads compare favorably with leading commercial microbeads of similar diameters. In addition, we are able to produce spherical beads in sizes ranging from 0.5 to 50 microns, enabling forces in the nN or even μN range in the larger sizes when paired with typical magnetic tweezer geometries. Larger beads may be useful in tissue-scale mechanical measurements (ex. wound healing) while the lack of autofluorescence makes the smaller beads ideal for microbead-based assays.