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    Optical non-contact localization of liquid-gas interfaces on disk during rotation for measuring flow rates and viscosities.

    Lab Chip 2012 Dec;12(24):5231-6
    Laboratory for MEMS Applications, Department of Microsystems Engineering-IMTEK, University of Freiburg, Georges-Koehler-Allee 103, Freiburg, 79110, Germany.
    We present a novel technique for the spatio-temporally resolved localization of liquid-gas interfaces on centrifugal microfluidic platforms based on total internal reflection (TIR) at the channel wall. The simple setup consists of a line laser and a linear image sensor array mounted in a stationary instrument. Apart from identifying the presence of usually unwanted gas bubbles, the here described online meniscus detection allows to measure liquid volumes with a high precision of 1.9%. Additionally, flow rates and viscosities (range: 1-12 mPa s, precision of 4.3%) can be sensed even during rotation at frequencies up to 30 Hz.
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