Three-Dimensional Integrated Ultra-Low-Volume Passive Microfluidics with Ion-Sensitive Field-Effect Transistors for Multiparameter Wearable Sweat Analyzers

Wearable systems could offer noninvasive and real-time solutions for monitoring of biomarkers in human sweat as an alternative to blood testing. Recent studies have demonstrated that the concentration of certain biomarkers in sweat can be directly correlated to their concentrations in blood, making sweat a trusted biofluid candidate for non-invasive diagnostics. We introduce a fully on-chip integrated wearable sweat sensing system to track biochemical information at the surface of the skin in real time. This system heterogeneously integrates, on a single silicon chip, state-of-the-art ultra-thin body (UTB) fully-depleted silicon-on-insulator (FD-SOI) ISFET sensors with a biocompatible microfluidic interface, to deliver a “Lab-on-skinTM” sensing platform. A full process for the fabrication of this system is proposed in this work and demonstrated by standard semiconductor fabrication procedures. The system is capable of collecting small volumes of sweat from the skin of a human, and posteriorly passively driving the biofluid, by capillary action, to a set of functionalized ISFETs for analysis of pH level and Na+ and K+ concentrations. Drop-casted Ion Sensing Membranes (ISM) on the different sets of sensors on the same substrate enables multi-parameter analysis on the same chip, with small and controlled cross-sensitivities, while a miniaturized Quasi-Reference Electrode (QRE) sets a stable analyte potential, avoiding the use of a cumbersome external Reference Electrode (RE). The progresses on Lab-on-SkinTM technology reported here can lead to autonomous wearable systems enabling real-time continuous monitoring of the sweat composition, with applications ranging from medicine to lifestyle behavioral engineering and sports.