Surface plasmon resonance biosensing based on target-responsive mobility switch of magnetic nanoparticles under magnetic fields

A novel surface plasmon resonance (SPR) detection technique based on the programmed assembly of superparamagnetic iron oxide nanoparticles (SPIONs) and the corresponding change in mobility under external magnetic fields was demonstrated. In this approach, SPIONs act as a magnetophoretic mobility switch undergoing aggregation only in the presence of target analytes. The aggregated SPIONs which were magnetically attracted to a metal film create a layer over the sensor surface with a refractive index contrast, resulting in a notable SPR angle change. The experimental results indicated that the concentrations of the reactants such as SA and the size of the SPIONs play important roles in achieving enhanced SPR sensing. As a result, this study illustrates the potential for sensitive and selective detection of target molecules without the requirement of immobilized receptors on the sensor surface.