Wearable System with Integrated Passive Microfluidics for Real-Time Electrolyte Sensing in Human Sweat

Wearable systems embodied as patches could offer noninvasive and real-time solutions for monitoring of biomarkers in human sweat as an alternative to blood testing, with applications in personalized and preventive healthcare. Sweat is considered to be a biofluid of foremost interest for analysis due the numerous biomarkers it contains. Recent studies have demonstrated that the concentration of some of these biomarkers in sweat, such as the electrolytes studied in this work, can be directly correlated to their concentrations in blood, making sweat a trusted biofluid candidate for non-invasive diagnostics. Until now, the biggest impediment to on‐body sweat monitoring was the lack of technology to analyze sweat composition in real‐time and mainly to continuously collect it. The goal of this work was to develop the building blocks of such wearable system for sweat electrolyte monitoring, with main emphasis on the passive microfluidics, the integrated miniaturized quasi-reference electrode and the functionalization of the sensing devices. The basic sensor technology is formed by Ion Sensitive Field Effect Transistors (ISFET) realized in FinFET and ultra-thin body Silicon on Insulator technology. This thesis shows the development of a state-of-the-art microsystem that allows multisensing of pH, Na+, K+ electrolyte concentrations in sweat, with high selectivity and high sensitivities (≈50 mV/dec for all electrolytes), in a wearable fashion. The microsystem comprises a biocompatible skin interface that collects even infinitesimal quantities of sweat (of the order of hundreds of picoliters to tenths of nanoliters), which the body produces in periods of low physical effort. One of the main achievements of this work is the integration of Ion Sensing Fully Depleted FETs and zero power consumption microfluidics, enabling low power (less than 50 nWatts/sensor) wearable biosensing. The thesis presents the needed technological processes and optimizations, together with their characterization, in order to achieve a Lab-On-Skin system.