Developing a video tracking method to study interactions between close pairs of optically trapped particles in three dimensions

We develop a video tracking method that utilizes an interpolation-based normalized cross-correlation approach to track the position of microscopic spherical particles in three dimensions. Subnanometer resolution is demonstrated. The method does not assume that the particle’s image is radially symmetric, making it useful for determining the position when particles are close and their images overlap. This is demonstrated in a study of the electrostatic and hydrodynamic interactions between a pair of beads in dual laser tweezers traps.