Multimodal Sweat Ion and Sweat Rate Sensing with Inkjet-printed Flexible Bracelet and Paperfluidics

Abstract

Sweat represents an optimal candidate for body chemistry analysis due to its rich composition and accessible collection without the need for invasive sampling. Although several examples of miniaturized potentiometric ion selective electrodes (ISE) have been proposed over the years, several challenges remain concerning the long-term stability and the influence of physical sweat parameters, such as dependencies on sweat rate and temperature. To improve the reliability of the measurements, a multi-parametric sweat analysis with socially discrete wearable packaging can represent a valuable strategy. Therefore, this work proposes a fully custom-designed flexible unit to simultaneously monitor three sweat parameters: ion concentration, temperature, and sweat gain/loss. The proposed intelligent medical bracelet is fabricated on a soft material with a high-resolution inkjet printing technique using commercially available engineered AgNP ink. After describing the design and fabrication of the system, an in-vitro characterization of each sensor is provided, employing a low cost soft paperfluidics, optimal for future applications in vivo. Measurements performed on ISE showed good reversibility and stability during continuous K+ monitoring. Calibration performed for both sweat rate and temperature sensors confirmed the accuracy of the customized circuit. Overall, presented results represent an essential starting point for future implementation in vivo of the prototype.