Characterizing the physicochemical properties of magnetic nanoparticles by a surface plasmon resonance approach

Magnetic nanoparticles (MNPs) are widely recognized as effective signal amplifiers for surface plasmon resonance (SPR)-based biosensors. Herein, we report that SPR sensors can be a useful tool to characterize the physicochemical properties of surface-functionalized iron oxide MNPs. In this work, a Kretschmann configuration-based SPR sensing platform with a scanning angular range of up to 17° is employed to identify the resonance conditions of different MNP suspensions. We demonstrate the feasibility of SPR for differentiating different surface coatings on the iron oxide MNPs, such as amine, biotin, and streptavidin, as well as distinguishing different magnetic core sizes (from 15 nm to 30 nm) and nanoparticle concentrations (from 0.013 mg/ml to 2.5 mg/ml). The SPR resonance angle shift, Δθ, is used as a crucial parameter for characterizing these physicochemical properties of MNPs floating within the surface of the metal layer that can directly interact with the surface plasmons, and the variation of their physicochemical properties is the reason causing a shift in the SPR resonance angle.