Optomagnetic detection technology reveals nanoparticle cluster geometries in biomarker assays

We investigate a fast and sensitive optomagnetic bionanotechnology for the detection of biomarkers. Antibody-coated superparamagnetic particles capture target molecules from solution and a magnetic field is used to align particles in chains. Dependent on the particle functionalization and particle concentrations, biochemical recognition leads to particle clusters of various geometries that remain after the magnetic field is turned off. Particle clusters can be detected with sub-picomolar sensitivity using a rotating magnetic field which induces an oscillating cross section for light scattering [Ranzoni et al, Nanoletters 2011 & ACS Nano 2012]. In this work we investigate the frequency components of the scattered light in order to unravel how clusters with different geometries contribute to the signal. To obtain these geometries, we control the inter-particle distances and cluster size by assays with DNA target molecules. The appearance of higher harmonics will be discussed and shown to depend on the assay format and the scattering angle.