MEMS Cavity-Based pH Image Biosensor for Wound Dressings to Monitor Hard-to-Cure Wounds

The biochemical processes in the body, including wound healing, are influenced by pH. When skin is damaged, in the inflammation phase, the pH of the skin is under pH 6.0, and in the granulation and spontaneous reepithelization phase, the pH of the skin oscillates between 6 and 8. If there is a frequent change in the wound dressing, it will make the damage to the skin hard to cure, especially for chronic wounds. In this article, we design and implement a highly sensitive micro-electro-mechanical-system (MEMS) cavity-based pH image biosensor of a $100\times100$ array with an integrated readout circuit in a CMOS bulk technology. Based on the proposed pH fringing electrical field model, we predict and optimize the performance of the proposed sensor pattern with cavity structure for operation frequency and various pH ions. The proposed pH biosensor with MEMS cavity structure exhibits a high sensitivity of 201 mV/pH, low drift voltage over time of 2.08 mV, a fast response time of 5 s, high precise repetition of 98.9%, and a pH image of 20 frame rate/s. Since the sensor is a $100\times100$ array, it displays a detailed change in the pH image of wound exudate to identify the inflammation stage under pH 6 or spontaneous reepithelization above pH 6 to indicate the need to change the dressing, reducing the clinician's wasted resources on frequency change of wound dressings.