A silicon master wafer patterned with the microfluidic structures was fabricated by standard photolithography as reported previously,34 (link) followed by elastomer molding via soft lithography. Briefly, the PDMS silicon elastomer base and curing agent were mixed at a 10:1 ratio (w/w), poured onto the master wafer, degassed under vacuum, and cured in an oven for at least 4 h at 80 °C. The PDMS mold was then peeled off the master wafer, resulting in channels with a depth of 10 µm. Then, 2 mm diameter reservoirs were manually punched at the channel ends. The PDMS slab was cleaned in isopropanol and distilled water and a glass slide was cleaned in acetone, isopropanol, and distilled water in an ultrasonic bath and dried in a stream of nitrogen. The slide and PDMS slab were subsequently treated in an oxygen plasma (PDC-001; Harrick Plasma, Ithaca, New York, U.S.A.) at high RF for 1 min. After treatment, the PDMS mold was irreversibly bonded to the glass slide to form a sealed microchannel system.