Stretchable, Wireless Sensors and Functional Substrates for Epidermal Characterization of Sweat

TLDR

Materials and device designs used for monitoring other body fluids can be adapted to epidermal sweat analysis. This work develops ultrathin, stretchable wireless sensors on elastomeric substrates for epidermal sweat analysis. The system employs inductively coupled LC resonator sensors on elastomeric substrates that collect sweat via capillarity and detect volume and chemical composition through dielectric and colorimetric measurements. The devices exhibit skin‑like elasticity, measure sweat volume with 0.06 μL mm⁻² accuracy, and provide colorimetric detection of pH and ion concentrations.

Abstract

This paper introduces materials and architectures for ultrathin, stretchable wireless sensors that mount on functional elastomeric substrates for epidermal analysis of biofluids. Measurement of the volume and chemical properties of sweat via dielectric detection and colorimetry demonstrates some capabilities. Here, inductively coupled sensors consisting of LC resonators with capacitive electrodes show systematic responses to sweat collected in microporous substrates. Interrogation occurs through external coils placed in physical proximity to the devices. The substrates allow spontaneous sweat collection through capillary forces, without the need for complex microfluidic handling systems. Furthermore, colorimetric measurement modes are possible in the same system by introducing indicator compounds into the depths of the substrates, for sensing specific components (OH(-) , H(+) , Cu(+) , and Fe(2+) ) in the sweat. The complete devices offer Young's moduli that are similar to skin, thus allowing highly effective and reliable skin integration without external fixtures. Experimental results demonstrate volumetric measurement of sweat with an accuracy of 0.06 μL/mm(2) with good stability and low drift. Colorimetric responses to pH and concentrations of various ions provide capabilities relevant to analysis of sweat. Similar materials and device designs can be used in monitoring other body fluids.