Force-compensated hydrogel-based pH sensors

Hydrogel-based pH sensors using bending plate transducers are attractive candidates for the pH measurement due to their high reliability, simple structure and their unnecessary reference and counter electrodes. However, their response time and long-term stability are often limited by the slow cooperative diffusion process within the hydrogels. To overcome this drawback, a sensor with force compensation is developed. This novel concept capitalizes on the fact that a compensation pressure arising from an actuator can suppress the hydrogel¿s swelling, accelerate the diffusion process within the hydrogel and, eventually, improve the sensor¿s dynamic behaviour.

This work aims at miniaturizing force-compensated pH sensors with improved sensor performance. In particular, a thermal microactuator with a high energy density is applied to replace macroscopic actuators used in the past. All sensor components are manufactured by microfabrication techniques, which reduce the sensor size and extend the application fields of this type of sensor. Both simulation and experimental results show that such sensors offer an expanded pH range, a higher sensitivity, and a much shorter response time than conventional open-loop sensors.