Calcite-assisted Localization and Kinetics (CLocK) microscopy

Calcite is a birefringent crystal, which means it can split light into an ordinary (o) ray, which follows the original path of the light, and an extraordinary (e) ray, which is spatially displaced. This transforms a single diffraction limited spot into two diffraction-limited spots, each with mutually perpendicular polarization. By rotating the calcite crystal, the position and polarization of the e-ray will move around the stationary o-ray. Setting the integration time of the camera to the rotation time of the crystal results in the e-ray forming a polarization-resolved ring. For isotropic objects that scatter light with equal intensity in all directions (like spheres), the ring will appear solid (particle 2), but for anisotropic objects with preferential scattering axes (like rods), the intensity modulate, with the highest scattering along the long axis of the rods (particles 1, 3-5).

A big advantage of CLocK is that it is compatible with in situ and in operando imaging, allowing us to monitor dynamic changes in nanoparticle structure (whether intended or not) and gain better understanding of structure-function relationships.  For example, we can track the time-dependent transformation of a gold nanorod to a gold nanosphere during chemidissolution. Ongoing projects involve understanding both dissolution and growth of nanoparticles in electrochemical environments, as well as studies on how sample preparation and ligand exchange affect nanoparticle structure and performance.