Rapid and Controlled Transition of Magnetic Nano- to Micro-particles: A Useful Feature for Bioseparations

B.J. Nehilla, T.H. Schulte
Nexgenia, Inc, US

Keywords: magnetic nanoparticles, RAFT polymerization, responsive materials


This work describes the use of stimuli-responsive polymers to control the transition of magnetic nanoparticles (mNPs) to magnetic microparticles. Compared to magnetic microparticles, mNPs are advantageous for bioseparations (e.g., immunoassays, immunoprecipitations) for two reasons. They have a larger surface area:volume ratio, and they have favorable diffusion coefficients so they do not settle out of solution. Thus, mNPs can bind more target molecules than magnetic microparticles, and they can diffuse in a sample to interact with the target molecules. The major disadvantage of mNPs is that they can not be separated with a simple benchtop magnet. Here, the stimuli-responsive mNPs are <50nm in diameter, and they respond sharply to temperature stimuli by transitioning from a hydrophilic to hydrophobic state. This transition permits soluble mNPs to interact with target molecules at room temperature but allows rapid magnetic separation of aggregated particles at 37C. When combined with polymer-antibody conjugates, the stimuli-responsive mNPs are used to capture a clinically relevant disease biomarker (HIV-1 p24 capsid protein) from spiked human serum samples. This reagent system outperformed commercially available magnetic microparticle reagents in assay speed and capture efficiency.