Food-Based Capacitive Sensors Using a Dynamic Permittivity Change with Hydrogels Responsive to Hydrogen Peroxide

Recent advances in ingestible electronics have elucidated the chemical composition of the gastrointestinal tract. Most devices are typically assembled from nondegradable materials, which require surgery for removal in cases of retention. Thus, edible electronic components based on naturally derived materials have been developed. However, a disease-specific digestible sensor is difficult to construct due to the limited ingredients available. Here, a food-based capacitive sensor using large dielectric constant changes with excellent selectivity is proposed. The sensor uses a combination of an interlayer of an enzyme-containing degradable hydrogel, an insulator of food-based slippery liquid-infused porous surfaces, and Au/gelatin electrodes. In the enzymatic reaction, generated micro-bubbles change the permittivity of the capacitor dynamically. Compared to most approaches for capacitive sensors using swelling/shrinking of the interlayer, this simple method excels in a large permittivity change with selectivity associated with the enzymatic reaction. This sensor is potentially applicable to various gaseous reactions, such as redox reactions, weak acid release reactions, and thermal decomposition. The capacitive component works in the contact-free device as the resonator or sensor. Therefore, this study would open the way to human-friendly material-based wireless chemical sensors in healthcare or environmental domains.