Capillary flow experiments are described with fluorescent molecules, bacteria, and microspheres using fluorescence correlation spectroscopy as an analytical tool. The flow velocity in the microcapillary is determined by fitting autocorrelation traces with a model containing parameters related to diffusion and flow. The flow profile of pressure-driven flow inside a microcapillary is determined by using the fluorescence fluctuations of a small dye molecule. It was found that bacteria and microspheres are retarded in their flow by optical forces produced by the laser beam.
Kunst, B. H., Schots, A., & Visser, A. J. W. G. (2002). Detection of Flowing Fluorescent Particles in a Microcapillary Using Fluorescence Correlation Spectroscopy. Analytical Chemistry, 74(20), 5350-5357. https://doi.org/10.1021/ac0256742