On-chip microfluidic transport and bio/chemical sensing based on electrochemical bubble formation

On-chip microfluidic transport was achieved using only integrated microfluidic components, including two pumps and four valves; furthermore, optical biosensing was conducted on the chip following the mixing of solutions by diffusion in a mixing channel. The basic components for the pumps and valves were three-electrode systems and a polydimethylsiloxane (PDMS) diaphragm to separate the electrolyte solution from the sample solution in the microflow channel. For the pump, hydrogen bubbles were grown or shrunk around platinum black working electrodes on the walls of anisotropically etched through-holes in a silicon substrate. The volume change of the bubbles caused deformation of the PDMS diaphragm over the working electrode, and the solution in the flow channel was mobilized. The same principle was used to open or close the valves in the flow channels. Two different solutions were introduced from two injection ports and transported through the flow channels by sequential operation of the pumps and the valves. When the flows were stopped, we were able to mix the solutions in a mixing channel. To demonstrate the applicability of the microfluidic system to microanalysis systems, a solution containing an enzyme and another solution containing enzyme substrates were injected from two injection ports, mixed, and allowed to react in the mixing channel. Fluorometric detection of the progress of enzymatic reactions and quantitative analysis of hydrogen peroxide and l-glutamate were conducted.