On-chip pH-regulator and its application to bio/chemical sensing

An on-chip pH-regulator based on an irregular use of an electrochemical thin-film three-electrode system will be presented. The device is operated using only an ordinary potentiostat. A pH-sensitive electrode was used for the reference electrode, whereas a non-polarizable Ag/AgCl electrode was used for the working electrode. Auxiliary electrode was placed around the working electrode, which worked as an actuator electrode. A pH change of the solution in the reaction chamber increased the overpotential and then a large current was generated. Accompanying the electrolysis of water on the auxiliary electrode, the pH of the reaction chamber recovered to the initial value rapidly. Recovery of pH was rapid and the pH in the reaction chamber could be controlled. The device could be used for the titration of an acid or a base. Linear relationships were observed between the generated charge and the concentration of analytes including acetic acid, ammonia, and urea. The output values were not affected by the buffering capacity.