Title: Spectroscopy, Physics, and Imaging Enabled by 3D Single-Particle Active-Feedback Tracking

Abstract:

The conventional idea of experimental physical chemistry has been to interrogate molecules under well-defined, usually pristine conditions. An interesting direction to advance experimental physical chemistry is to be able to study chemical dynamics in situ—complex systems that are highly heterogeneous both in space and time. The active feedback-based 3D single-particle μs tracking technique was developed in order to achieve this overarching goal. The technique affords time-dependent single-particle spectroscopy of a freely moving nanoparticle with 10 μs time resolution and <10 nm three-dimensional localization precision. With concurrently developed theories, it enables single-particle dynamic light scattering spectroscopy, which in turn allows the direct measurements of the size, the shape, and the sub-millisecond translation-rotation dynamics of individual fast-moving nanoparticles with a precision that reaches information-theory bounds. The approach also enables experimentally testing basic theoretical concepts that have eluded scientists. Examples include the “hot Brownian motion” theory which describes the random-walk dynamics of a nano-object under far-from equilibrium conditions. Another classical colloidal physics problem is nanoscale direction-dependent diffusivity divergence near a rigid wall. In addition to validating theoretical predictions, the 3D μs tracking technique has also enabled the concept of multi-resolution imaging, which is finding real-life applications in virology and drug delivery.