Electrochemically actuated microvalves for microfluidic systems

Electrochemical actuation is used to make active control elements for microfluidic applications that require no moving mechanical parts. Electrochemical bubbles were generated directly inside the micro-channels, which serve as valves. Bubble formation and its physical interaction with the fluid were visualized using epi-fluorescent microscopy, which shows that the valve completely stops the flow. Valve closing/opening was quantitatively characterized for flow rates ranging from ≈5 mm/s to 27 mm/s (inlet pressures 102 kPa to 105 kPa). It was found that valves could be closed/opened in relatively short times (≈30 ms) and consume low power (≈10 μJ). The current versus time curves measured at progressively higher voltages (from 3.8 V to 5.2 V) shows a linear relationship between the total charges transferred during electrolysis and the resulting bubble size. The large volume change associated with liquid to gas transformation can also be used to displace liquid for dosing or pumping.