Impact of protein corona on magnetic particle spectroscopy-based bioassays.

Magnetic nanoparticles (MNPs) can be functionalized with targeting ligands to give them an affinity for a biomolecule of interest. Functionalized MNPs (fMNPs) can aggregate in the presence of a multivalent target, causing a change in their magnetization. The 3rd harmonic phase of the fMNP magnetization signal can be proportional to the multivalent target concentration. When fMNPs are suspended in protein rich media (like biological fluids), off-target proteins tend to non-specifically adsorb to them, potentially masking their targeting ligands, and leading to a change in fMNP target affinity. The layer of adsorbed off-target proteins is commonly referred to as a protein corona. We used a model system consisting of biotinylated MNPs that target streptavidin to study the impact of protein corona formation on fMNP-based biosensing. Interestingly, the resolution of our biotinylated MNP-based aggregation assay changed from 64.43 nM streptavidin in the absence of off-target serum proteins, to 3.22 nM streptavidin in the presence of off-target serum proteins. Therefore, biotinylated MNP streptavidin sensitivity increased in the presence of off-target serum proteins. We attribute the increase in biotinylated MNP streptavidin sensitivity to competition between streptavidin and off-target serum proteins with a low biotin binding affinity. In contrast, competition between streptavidin and an off-target protein with a high biotin binding affinity decreased biotinylated MNP streptavidin sensitivity. Our results can be leveraged to inform the design optimization of an in vivo fMNP-based biosensor. Additionally, our results can also be leveraged to design an in vitro fMNP-based biosensor with a diluent off-target protein concentration and binding affinity optimal for target quantification in a tailored range.