Research in my laboratory focuses on manipulating particles in colloidal suspensions using light. Colloidal suspensions, such as paint, consist of small particles (typically, at least 10 times smaller than the diameter of a human hair!) suspended in a fluid. The particles are large enough, however, to interact strongly with light and can often be seen under a microscope. The ability to image and manipulate particles in colloidal suspensions makes them excellent model systems for studying complex phenomena such as how crystals melt or how cell membranes self-assemble. We study how colloidal particles can be manipulated with light by combining experiments and computational modeling.
Experiments: manipulating non-spherical particles using optical tweezers
Optical tweezers use a focused laser beam to exert and measure forces on colloidal particles -- like tractor beams in science fiction movies, albeit on a microscopic scale. Optical tweezers can be used to measure the forces exerted by biological molecules, assemble objects at the nanoscale, and study how colloidal particles interact with each other.
Trapping spherical particles is relatively straightforward and well-understood. Understanding how non-spherical particles (such as cylinders or clusters of spheres) behave in optical tweezers is much harder. Under what conditions can such particles be trapped? How will they orient themselves if they are trapped? Can we control how they are oriented?
My students and I are building an optical tweezers microscope to answer these questions. By combining optical tweezers and a three-dimensional imaging technique called holographic microscopy, we will be able to examine in detail how non-spherical particles behave in optical tweezers. We will then explore how generating multiple trapping beams using a technique known as holographic optical tweezers might enable particles such as ellipsoids to be trapped in arbitrary orientations.
Computation: modeling optical tweezers and light scattering
In parallel to our experiments, we are using computer models of how small particles interact with light (namely, what is known as a T-matrix approach) to calculate how non-spherical particles behave in optical tweezers. We plan to compare the computational results with our experiments.
We are also developing software that will use advanced data analysis techniques (such as Bayesian inference) to interpret data from light scattering experiments.