Soft, Skin‐Interfaced Microfluidic Systems with Passive Galvanic Stopwatches for Precise Chronometric Sampling of Sweat

Abstract

Comprehensive analysis of sweat chemistry provides noninvasive health monitoring capabilities that complement established biophysical measurements such as heart rate, blood oxygenation, and body temperature. Recent developments in skin‐integrated soft microfluidic systems address many challenges associated with standard technologies in sweat collection and analysis. However, recording of time‐dependent variations in sweat composition requires bulky electronic systems and power sources, thereby constraining form factor, cost, and modes of use. Here, presented are unconventional design concepts, materials, and device operation principles that address this challenge. Flexible galvanic cells embedded within skin‐interfaced microfluidics with passive valves serve as sweat‐activated “stopwatches” that record temporal information associated with collection of discrete microliter volumes of sweat. The result allows for precise measurements of dynamic sweat composition fluctuations using in situ or ex situ analytical techniques. Integrated electronics based on near‐field communication (NFC) protocols or docking stations equipped with standard electronic measurement tools provide means for extracting digital timing results from the stopwatches. Human subject studies of time‐stamped sweat samples by in situ colorimetric methods and ex situ techniques based on inductively coupled plasma mass spectroscopy (ICP‐MS) and chlorodimetry illustrate the ability to quantitatively capture time‐dynamic sweat chemistry in scenarios compatible with field use.

A Mediator‐Free Electroenzymatic Sensing Methodology to Mitigate Ionic and Electroactive Interferents' Effects for Reliable Wearable Metabolite and Nutrient Monitoring

“…These ionic species include hydrated cations with smaller radii, such as K + (0.125 µm), Rb + (0.128 µm), Cs + (0.119 µm), and NH 4 + (0.125 µm) . Among these cations, K + is of particular importance in wearable biomarker sensing applications due to its high abundance and inter/intrasubject variation in sweat …”

Wireless battery-free body sensor networks using near-field-enabled clothing

“…Current solutions for wireless sensor interconnection either require each sensor to be independently powered (such as with batteries) 11,[17][18][19][20][21][22][23] or have a very limited range of operation (few centimetres) [32][33][34][35][36][37][38][39] . Networks of skin-mountable sensors use.…”

“…Near-field communication (NFC) is an alternative wireless technology in which sensors are inductively powered by a wireless reader 25,31 . Because NFC-based sensors can be battery-free, low-cost, and secure against eavesdropping, this technology has emerged as a versatile platform for developing skin-mounted or implanted electronics capable of measuring heart rate, tissue oxygenation, sweat electrolyte composition, ultraviolet light exposure, and other physiological parameters [32][33][34][35][36][37][38][39] . A major limitation of NFC technology, however, is that the sensors can function only within the near-field of the reader, which is at most a few centimetres for a mobile reader such as a smartphone 25,31 .…”

Wireless, Battery‐Less Biosensors Based on Direct Electron Transfer Reactions

“…Biofuel cells might be good battery alternatives for short‐term (days, up to few weeks) operating devices. However, the devices are still rich with semiconductor elements and, thus, are considered as a reusable sensor platforms . Benefits provided by DET of enzymes are probably negligible in such sensor devices, which rely on potentiostats.…”