Spatially extended FCS for visualizing and quantifying high-speed multiphase flows in microchannels

We report the development of spatially extended fluorescence correlation spectroscopy for visualizing and quantifying multiphase flows in microchannels. We employ simultaneous detection with a high-speed camera across the width of the channel, enabling investigation of the dynamics of the flow at short time scales. We take advantage of the flow to scan the sample past the fixed illumination, capturing frames up to 100 KHz. At these rates, we can resolve the motion of sub-micron particles at velocities up to the order of 1 cm/s. We visualize flows with kymographs and quantify velocity profiles by cross-correlations within the focal volume. We demonstrate the efficacy of our approach by measuring the depth-resolved velocity profile of suspensions of sub-micron diameter silica particles flowing up to 1.5 mm/s.