Adhesive RFID Sensor Patch for Monitoring of Sweat Electrolytes

TLDR

Wearable digital health devices are predominantly rigid, such as bracelets and pucks. The authors present an adhesive RFID sensor patch that adheres intimately to skin for continuous sweat biomarker monitoring. The patch integrates a commercial RFID chip with minimal circuitry on a flexible Cu/polyimide layer, enabling potentiometric sensing of sweat solutes and temperature via an Android app with 96 % accuracy at 50 mM Na⁺, and optionally uses paper microfluidics to wick sweat. The patch remained wearable for seven days, resembling a standard Band‑Aid, and demonstrated hydration monitoring while being extendable to other millimolar sweat ions such as Cl⁻, K⁺, Mg²⁺, NH₄⁺, and Zn²⁺.

Abstract

Wearable digital health devices are dominantly found in rigid form factors such as bracelets and pucks. An adhesive radio-frequency identification (RFID) sensor bandage (patch) is reported, which can be made completely intimate with human skin, a distinct advantage for chronological monitoring of biomarkers in sweat. In this demonstration, a commercial RFID chip is adapted with minimum components to allow potentiometric sensing of solutes in sweat, and surface temperature, as read by an Android smartphone app with 96% accuracy at 50 mM Na(+) (in vitro tests). All circuitry is solder-reflow integrated on a standard Cu/polyimide flexible-electronic layer including an antenna, but while also allowing electroplating for simple integration of exotic metals for sensing electrodes. Optional paper microfluidics wick sweat from a sweat porous adhesive allowing flow to the sensor, or the sensor can be directly contacted to the skin. The wearability of the patch has been demonstrated for up to seven days, and includes a protective textile which provides a feel and appearance similar to a standard Band-Aid. Applications include hydration monitoring, but the basic capability is extendable to other mM ionic solutes in sweat (Cl(-), K(+), Mg(2+), NH4(+), and Zn(2+)). The design and fabrication of the patch are provided in full detail, as the basic components could be useful in the design of other wearable sensors.