(132f) Towards Total Internal Reflection Microscopy of Anisotropic Particles

Total internal reflection microscopy (TIRM) is used to measure the Brownian fluctuations in distance between a colloidal particle and a surface illuminated by an evanescent wave. For non-spherical particles, the intensity fluctuations that would normally arise from changes in separation distance also result from variations in the orientation of the particle with respect to the evanescent wave propagation vector. Hence, in order to retrieve the particle-surface separation distance, it is necessary to decouple the contribution of orientation changes from the total scattered light intensity. Here we present experiments of ellipsoidal particles deposited on a surface at random orientations under camera-based TIRM. We recorded scattering images of these colloidal particles and then used a two-dimensional Gaussian function to characterize the scattering morphology, an approach we name “Scattering Morphology Resolved Total Internal Reflection Microscopy (SMR-TIRM)". We measured how the distortions in the scattering images relate to the particle orientation, and local geometry. In addition, we compared our experimental results with simulated scattering images obtained by the T-Matrix method, which can be used to decouple the contribution of the polar and azimuthal angles in the total intensity, and systematically explore how the local geometry affects the scattering morphology. The scattering morphology and the scattering intensity relations could be used to probe the three-dimensional orientation of the particle and the particle-surface separation distance. We aim to use this method to extend the capabilities of TIRM to measure the interaction energy between an anisotropic colloid and a flat plate.