Electrochemical pH-responsive valve for automatic sampling

To realize automatic sampling of a solution sensing the pH, a pH-responsive valve that operates using a nonstandard electrochemical three-electrode system was fabricated. A pH-sensitive electrode was used as a reference electrode, and a working electrode or an auxiliary electrode was used as a valve electrode depending on the direction of the pH change. The potential of the reference electrode changed with the increase or decrease of the pH, resulting in a change in the wettability of the valve electrode. By adjusting the voltage applied to the working electrode, the valve opened at pHs higher or lower than a threshold value. By combining two types of valves that opened in the acidic and basic regions, a pH filter that passed only a solution of a limited pH range could also be realized. Furthermore, the pH-responsive valve could also be used to form valves that sensed biochemical molecules and opened at concentrations higher than a threshold.