Methods of Digital Video Microscopy for Colloidal Studies

John C. Crocker and David G. Grier


We describe a set of image processing algorithms for extracting quantitative data from digitized video microscope images of colloidal suspensions. In a typical application, these direct imaging techniques can locate submicron spheres to within 10 nm in the focal plane and 150 nm in depth. Combining information from a sequence of video images into single-particle trajectories makes possible measurements of quantities of fundamental and practical interest such as diffusion coefficients and pair-wise interaction potentials. The measurements we describe in detail combine the outstanding resolution of digital imaging with video-synchronized optical trapping to obtain highly accurate and reproducible results very rapidly.

Keywords: colloid, image processing, video microscopy, optical tweezers, dynamics, diffusion coefficient, interaction potential

David G. Grier
Mon Mar 11 23:01:27 CST 1996