Flow profiles and directionality in microcapillaries measured by fluorescence correlation spectroscopy

We report hydrodynamic and electrophoretic flow profiling in microcapillaries using fluorescence correlation spectroscopy. We find that capillary electrophoresis results in various velocity profiles depending on capillary diameter - constant in small capillaries and parabolic in large ones-, while hydrodynamic flow velocity profile is Poiseuille like. The deviation from the expected electrophoretic constant flow profile in large capillaries is attributed to thermal effect. Furthermore, we propose and demonstrate a new method for flow directionality measurement using a non-symmetric transverse excitation beam profile.