Lab on skin^™: 3D monolithically integrated zero-energy micro/nanofludics and FD SOI ion sensitive FETs for wearable multi-sensing sweat applications

Abstract

This paper reports a novel fully integrated low power multi-sensing smart system, which, by wafer-level 3D heterogeneous integration of Ion Sensitive Fully Depleted (FD) FETs and SU-8 micro/nanofludics, achieves the first of its kind wearable multi-sensing system, called Lab on Skin TM , capable to detect biomarkers in human sweat. In the reported configuration, the multi-sensing system exploits arrays of functionalized sensors capable to simultaneously detect pH, Na + and K + concentrations in sweat in real time. We present a detailed electrical DC and dynamic characterization, showing excellent sensitivities (52mV/dec for pH and-37mV/dec for Na + sensors) with ultra-low power consumption (less than 50 nWatts/sensor). We report ion cross-sensitivities and a differential measurement approach that allows calibrated measurements. Overall, the paper reports significant advances in the design and fabrication of micro/nanofludics channels, inlets compatible with human skin pore size and density, and outlet passive pumps with flow rates of tens of pl/s; all capable of exploiting capillary forces in order to provide a zero energy pumping of sweat into sensing channels. Moreover, we report the first integration of a miniaturized Ag/AgCl Quasi-Reference Electrodes (QRE) into the sensing system, with long term stability, paving the way for fully wearable electronic chips in flexible patches or as plug-in modules in wrist based devices. I. INTRODUCTION AND RATIONALE Wearable biosensors [1-2] hold promise for playing a significant role in future personalized and preventive healthcare as they enable non-invasive and real time monitoring of a large variety of biomarkers in human biofluids. They add significant value to activity monitoring, which is tracked by MEMS sensor technology (accelerometers and gyroscopes), and, to other biosignals (such as heart rate and blood oxygenation). Moreover, sweat is easily accessible via the largest human organ, the skin, and can take advantage of patch and wrist-based device embodiments. Previous reports on the detection of biomarkers in sweat were based on large electrochemical sensors [3-4] requiring large amounts of sweat, which limits the field of applications to sport with abundant sweating or requires pilocarpine-induced cholinergic sweating, which is not user friendly and can even modify the physiological composition of sweat. A recent comprehensive review [5] reported that there are hundreds of biomarkers that can be tracked in human sweat and, for some, the correlations with the concentrations of same

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“…Indeed, integration of such thin-film transistors on flexible foils is straightforward, and power need is minimal. Following this strategy, Bellando et al [65] focused on the integration of IS-FDSOI with nanofluidics in SU-8 resin. They called their device the Lab on Skin™, able to simultaneously measure pH, Na + , and K + in sweat.…”