Skin-Attachable, Stretchable Electrochemical Sweat Sensor for Glucose and pH Detection

Abstract

As part of increased efforts to develop wearable healthcare devices for monitoring and managing physiological and metabolic information, stretchable electrochemical sweat sensors have been investigated. In this study, we report on the fabrication of a stretchable and skin-attachable electrochemical sensor for detecting glucose and pH in sweat. A patterned stretchable electrode was fabricated via layer-by-layer deposition of carbon nanotubes (CNTs) on top of patterned Au nanosheets (AuNS) prepared by filtration onto stretchable substrate. For the detection of glucose and pH, CoWO/CNT and polyaniline/CNT nanocomposites were coated onto the CNT-AuNS electrodes, respectively. A reference electrode was prepared via chlorination of silver nanowires. Encapsulation of the stretchable sensor with sticky silbione led to a skin-attachable sweat sensor. Our sensor showed high performance with sensitivities of 10.89 μA mM cm and 71.44 mV pH for glucose and pH, respectively, with mechanical stability up to 30% stretching and air stability for 10 days. The sensor also showed good adhesion even to wet skin, allowing the detection of glucose and pH in sweat from running while being attached onto the skin. This work suggests the application of our stretchable and skin-attachable electrochemical sensor to health management as a high-performance healthcare wearable device.

Recent Progress in Transparent Conductors Based on Nanomaterials: Advancements and Challenges

“…Metal‐based nanomaterials in the form of nanowires, nanoparticles and layered coatings have become extremely popular thanks to breakthroughs in synthesizing these nanomaterials 39–41. Metal nanomaterials such as silver,1,42–44 gold,45 and copper46 also have been used to successfully fabricate TCE. Current exploration in hybrid nanomaterials has gained the most attention with the ability to create a hierarchical nanocomposite that can address issues of junction resistance between nanomaterials and obtain a lower percolation threshold with lower concentration in addition to simultaneously combining the characteristics of two or more nanomaterials 47…”

Stretchable sensors for environmental monitoring

“…104 These tubes can be viewed as molecular-scale tubes formed from graphitic sheets with diameters ranging from a few nanometers to a few tens of nanometers, being semiconducting, metallic, or semimetallic depending on their chirality and diameter. 105 Because of their outstanding mechanical properties (such as high tensile strength and elastic modulus) and excellent electrical properties and chemical inertness, [106][107][108][109] CNTs have been widely used as filler materials for stretchable conductors and applied in stretchable environmental sensing devices such as light, 110 temperature, 80,111 pH, 112 and humidity sensors. 113,114 Several mixing methods (e.g., grinding, 29 jet milling, 30 and hotrolling 101 ) have been developed to obtain uniformly dispersed high-performance CNT-based stretchable conductors.…”

“…Because of the straightforward transduction principle and simple readout configuration, potentiometric pH sensors have been the dominant instrument used for pH sensing, including stretchable pH sensors. 112,121,188 The spectrometric pH sensor is an alternative sensing technique. Unlike electrochemical pH sensing, the spectrometric technique indirectly acquires the pH of a solution by measuring the concentration of the acidic and basic forms of the pH indicators.…”

“…PANI, known as a pH-sensitive conducting polymer, has received increasing attention as an ISE material for wearable, stretchable pH sensors because of its low cytotoxicity and low skin irritation. 112 On the other hand, accounting for the compatibility with Applied Physics Reviews REVIEW scitation.org/journal/are semiconductor device manufacturing processes, solid-state metal oxides, particularly iridium oxide, are considered to be a particularly advantageous ISE material. It has also other favorable properties such as high sensitivity (super-Nernstian responses to pH change), stability over a wide pH range, rapid response time, minimal potential drift, outstanding chemical selectivity, and high durability.…”

“…In 2018, Oh et al fabricated a PANI-based skin-attachable and stretchable electrochemical sensor that can detect pH in human perspiration. 112 A percolation network of Au nanosheets (Au NS) and CNTs was formed via vacuum filtering and a layer-by-layer method, respectively, on a stretchable substrate [ Fig. 7(c)] as the stretchable interconnect for the PANI working electrode and the Ag/AgCl reference electrode.…”