How fast does a nanomachine move? Can we watch it moving, if we can see it at all? What types of movements can we track at the nanoscale, and to what degree of spatial and temporal precision?

My thesis seeks to develop the necessary theoretical and experimental framework to answer these questions through the lens of a specialized optical microscopy technique known as interferometric scattering (iSCAT), first demonstrated in the early 2000s.

To establish the theoretical limits of nanoscale optical tracking, I derive theories of iSCAT imaging yielding fully quantitative predictions in good agreement with existing published results, reporting a universal equation that predicts the contrast of a small scattering particle in any iSCAT setup without the need for prior calibration.

For practical analysis of high-speed iSCAT videos, I devise a particle tracking algorithm and implement it in original computer code. Testing its performance on my iSCAT videos of freely diffusing nanoparticles recorded at over 10,000 frames per second, I verify its ability to localize fast-moving objects in three dimensions to precisions of tens of nanometers.

Finally, I embark on a theoretical exploration of symmetry and symmetry breaking in iSCAT images, elucidating the origins of unusual spiral point-spread functions seen in my simulations and experiments. These supporting experiments are performed on my custom-designed and home-built polarized iSCAT microscope, which also allows for continuous tuning of the iSCAT contrast from the standard bright-field mode to a novel dark-field mode.

I anticipate that this contribution to advancing the theoretical understanding and practical applicability of iSCAT may accelerate its adoption for high-speed precision tracking of nanoscale motion in a variety of nanoscale and biophysical contexts, including pioneering research into DNA origami nanomachines.