A Wearable Skin Conformal Self Powered Tattoo Based Hydration Sensor Using Graphene and Clay Nanosheet Membranes

We present an innovative, self-powered tattoo sensor crafted from a vermiculite clay nanosheet membrane layered with graphene. Sweat is a critical indicator of hydration status, helping the body regulate temperature, and can also signal potential health issues, including dehydration and electrolyte imbalances. Therefore, it is important to continuously monitor sweat levels as a surrogate for hydration level. In this study, we have developed a wearable tattoo sensor, paired with a semi-custom circuit, that monitors sweat humidity changes as they relate to an individual's hydration status. Notably, no external power source is required where the sensor serves as a sweat moisture-based energy generator. The developed moist energy generator from sweat has a power density of 7.16 nW/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. By measuring real-time output from this energy harvester, this sensor has the potential to provide an indication of hydration levels, that may enable early intervention to prevent life-threatening conditions from dehydration.