Ultrathin, Self-Adhesive, Sweat-Absorbing Janus Membrane Epidermal pH Sensor

Wearable biomedical sensors have enabled non-invasive and continuous physiological monitoring for daily health management and early detection of chronic diseases^[1,2]. Among the biomedical sensors, wearable pH sensors attracted significant interest as pH influences most biological reactions^[3,4]. However, the conformable pH sensor which can be self-adhesive to human skin, has sweat-wicking ability and gas permeability remains largely unexplored. Here, we present a novel approach to this problem through the development of a Janus membrane-based pH sensor with self-adhesive on the skin. The sensor consists of a hydrophobic polyurethane-polydimethylsiloxane (PU-PDMS) porous nanometer-thick film and a hydrophilic polyvinyl alcohol-polyacrylic acid (PVA-PAA) nanofiber film. This Janus membrane exhibits a thickness of a few micrometers, providing a firm and comfortable adhesion to the skin. The sensor demonstrates fast-responsive, accurate, and long-term pH measurements, enabling reliable wearable applications. The simultaneous realization of solution absorption, gas-permeability, and self-adhesiveness, make it suitable for long-term, continuous monitoring without compromising wearer comfort. The pH sensor has been tested successfully for continuous monitoring over an hour, demonstrating its potential for stable analysis of skin health conditions. This innovative Janus membrane-based pH sensor holds significant promise for comprehensive skin health monitoring and wearable biomedical applications.<br/><br/><b>Reference</b><br/>[1] T. R. Ray, J. Choi, A. J. Bandodkar, S. Krishnan, P. Gutruf, L. Tian, R. Ghaffari, J. A. Rogers, Bio-integrated wearable systems: A comprehensive review.<i> Chem Rev.</i> 119 (2019), pp. 5461–5533.<br/>[2] Y. Luo et al., Technology Roadmap for Flexible Sensors.<i> ACS Nano.</i> 17 (2023), pp. 5211–5295.<br/>[3] S. Nakata, M. Shiomi, Y. Fujita, T. Arie, S. Akita, K. Takei, Nat Electron. 1, 596–603 (2018).<br/>[4] A. Koh, D. Kang, Y. Xue, S. Lee, R. M. Pielak, J. Kim, T. Hwang, S. Min, A. Banks, P. Bastien, M. C. Manco, L. Wang, K. R. Ammann, K.-I. Jang, P. Won, S. Han, R. Ghaffari, U. Paik, M. J. Slepian, G. Balooch, Y. Huang, J. A. Rogers, “A soft, wearable microfluidic device for the capture, storage, and colorimetric sensing of sweat” (2016).