Visualization of flow patterning in high-speed centrifugal microfluidics

Abstract

This work presents a new experimental setup for image capturing of centrifugally driven flows in disk-based microchannels rotating at high frequencies of up to 150Hz. To still achieve a micron-scale resolution, smearing effects are minimized by a microscope-mounted CCD camera featuring an extremely short minimum exposure time of 100ns, only. The image capture is controlled by a real-time PC board which sends delayed trigger signals to the CCD camera and to a stroboscopic flash upon receiving the zero-crossing signal of the rotating disk. The common delay of the trigger signals is electronically adjusted according to the spinning frequency. This appreciably improves the stability of the captured image sequences. Another computer is equipped with a fast framegrabber PC board to directly acquire the image data from the CCD camera. A maximum spatial resolution ranging between 4.5μm at rest and 10μm at a 150Hz frequency of rotation is achieved. Even at high frequencies of rotation, image smearing does not significantly impair the contrast. Using this experimental setup, the Coriolis-induced patterning of two liquid flows in 300-μm-wide channels rotating at 100Hz is visualized at a spatial resolution better than 10μm.