A rotating molecular ruler : detection of particle-particle distance in an optomagnetic cluster assay

We investigate a fast and sensitive optomagnetic bionanotechnology for biomarker detection. Antibody-coated superparamagnetic particles capture biomarker molecules and form clusters with a biomarker molecule sandwiched between two particles. These particle clusters can be analyzed using a rotating magnetic field which induces an oscillating light scattering cross-section, resolving sub-picomolar biomarker concentrations [Ranzoni et al, Nanoletters 2011; ACS Nano 2012]. In this paper we report a method to quantify the particle-particle distance with nanometer resolution. Simulations of the light scattering by rotating clusters show that the high-frequency components hold detailed information about the geometry of the particle clusters, including a strong dependence on the inter-particle distance. We will report the simulation results and experimental data of model cluster assays.