Orthogonal Nanoparticle Size, Polydispersity, and Stability Characterization with Near-Field Optical Trapping and Light Scattering

Abstract

Here we present and demonstrate a new technique for simultaneously characterizing the size, polydispersity, and colloidal stability of nanoparticle suspensions. This method relies on tracking each nanoparticle’s motion in three spatial dimensions as it interacts with the evanescent field of an optical waveguide. The motion along the optical propagation axis of the waveguide provides insight into the polydispersity of a nanoparticle suspension. Horizontal motion perpendicular to the propagation axis gives the diffusion coefficient and particle size. In the direction normal to the surface, statistical analysis of the scattered light intensity distribution gives a map of the interaction energy landscape and insight into the suspension stability. These three orthogonal measurements are made simultaneously on each particle, building up population level insights from a single-particle rather than ensemble-averaged basis. We experimentally demonstrate the technique using polystyrene spheres obtaining results con...