Determining the Spheroid Geometry of Individual Metallic Nanoparticles by Two-Dimensional Single-Particle Dynamic Light Scattering

Single-particle dynamic light scattering (SP-DLS) is a recently developed technique that uses dark-field illumination, active real-time three-dimensional single-particle tracking, and measurements of scattered photon polarizations to nonperturbatively evaluate the shapes of single, freely diffusing particles under the assumption of the particle having either prolate or oblate spheroid geometry. As originally developed, however, SP-DLS is incapable of unambiguously assigning either of these geometries to a single particle. In this contribution, we resolve this ambiguity by introducing a second experimental observable-the scattering spectrum-so that both the scattering polarization and spectrum are simultaneously recorded and analyzed. We used numerical simulations of SP-DLS to characterize the performance of this new approach as well as the effects of key experimental parameters. We anticipate that the analyses presented here will not only form a straightforward guide for researchers seeking to optimize their own SP-DLS shape measurements but also serve as the basis for future studies of time-dependent reconfiguration in single nanostructures.