Conformal, waterproof electronic decals for wireless monitoring of sweat and vaginal pH at the point-of-care

While the monitoring of pH has demonstrated to be an effective technique to monitor an individual's health state, the design of wearable biosensors is subject to critical challenges, such as high fabrication costs, thermal drift, sensitivity to moisture, and the limited applicability for users with metal allergies. This work describes the low-cost fabrication of waterproof electronic decals (WPEDs): highly conformable disposable biosensors capable of monitoring sweat and vaginal pH. WPEDs contain a polyaniline/silver microflakes sensing layer optimized for accurate impedance-based pH quantification across the clinically relevant range of variation of most biofluids. WPEDs also contain a heating layer that serves to both stimulate sweating and prevent saturation of the sensing area, reducing the variability of the measurements. The conformability of WPEDs enables their simple and allergy-free attachment to skin, where they can monitor sweat pH, or to the surface of paper-based sample containers, for the pH-based diagnosis of bacterial vaginosis. WPEDs are mostly transparent, self-adhesive, breathable, flexible, moisture-insensitive, and able to maintain their accuracy under significant mechanical and thermal stresses. A cost-effective wearable and portable impedance analyzer wirelessly transmits pH data in real-time to the smartphone of the user, where a custom-developed App enables long term monitoring and telemedicine applications. Our results demonstrate the feasibility of using inexpensive single-use WPEDs and a reusable, wireless impedance analyzer to provide a wearable solution for the real-time monitoring of sweat pH and the accurate at-home diagnosis of bacterial vaginosis, improving the capabilities of current low-cost, point-of-care diagnostic tests.