In the field of sweat monitoring, many sensors have been piloted with one or two subjects over limited periods of time, but there is a need for prolonged, large-scale studies to establish reliable physiological correlations that account for diverse subjects, activities, and environments. Chemical sensors provide the concentration of analytes of interest, including sodium, potassium, and glucose, while sweat rate sensors provide standalone information on nerve function and hydration. Monitoring both of these in parallel will enable the decoding of concentrations of analytes that are modulated by sweat rate. We have developed a robust, wearable, continuous-time sweat sensing system including both flow rate sensor and chemical sensor channels. First, a microfluidic sweat rate sensor quantifies the flow rate of sweat without interference from variations in its ionicity using two fingered electrodes extending along the length of the channel. This measurement can be performed with a commercial benchtop LCR meter or a custom, wearable system. Using state-of-the-art integrated circuit components and Bluetooth Low Energy (BLE) for wireless communication with an Android app, the custom electronics are compact (<8cm2), low cost (<$40), and low power (<6mA). Additionally, the electronics system contains amperometry and potentiometry channels for continuous monitoring of sweat analytes. The described system is integrated into two form factors: (1) a reusable, wristwatch-like collection device to take up sweat from a well-defined area of skin, without leakage and with minimal lag from dead volume, and perform accurate, timely sweat rate measurement and (2) a small fingertip-mounted microfluidic device. Finally, the fluidic pattern ensures that sweat rate can be measured accurately for prolonged on-body wear over the range of secretion rates for the target application. Fabrication is done via roll-to-roll (R2R) processes, which are key for production at high throughputs and volumes. This includes R2R printing of ordered layers of conductive and insulating inks to define flow rate and chemical sensing electrodes, combined with R2R laser cutting to pattern microfluidic layers and spacers. Rigid gaskets can also be produced at scale through injection molding, and all components then rapidly assembled with adhesive tapes. Overall, we present a wearable, fully-integrated, continuous-time system for diverse sweat sensing applications.
Project currently funded by: Federal
Project temporarily suspended as of 08/01/2023