Carbon Nanotube-Based Ion Selective Sensors for Wearable Applications

Abstract

Wearable electronics offer new opportunities in a wide range of applications, especially sweat analysis using skin sensors. A fundamental challenge in these applications is the formation of sensitive and stable electrodes. In this article we report the development of a wearable sensor based on carbon nanotube (CNT) electrode arrays for sweat sensing. Solid-state ion selective electrodes (ISEs), sensitive to Na ions, were prepared by drop coating plasticized poly(vinyl chloride) (PVC) doped with ionophore and ion exchanger on CNT electrodes. The ion selective membrane (ISM) filled the intertubular spaces of the highly porous CNT film and formed an attachment that was stronger than that achieved with flat Au, Pt, or carbon electrodes. Concentration of the ISM solution used influenced the attachment to the CNT film, the ISM surface morphology, and the overall performance of the sensor. Sensitivity of 56 ± 3 mV/decade to Na ions was achieved. Optimized solid-state reference electrodes (REs), suitable for wearable applications, were prepared by coating CNT electrodes with colloidal dispersion of Ag/AgCl, agarose hydrogel with 0.5 M NaCl, and a passivation layer of PVC doped with NaCl. The CNT-based REs had low sensitivity (-1.7 ± 1.2 mV/decade) toward the NaCl solution and high repeatability and were superior to bare Ag/AgCl, metals, carbon, and CNT films, reported previously as REs. CNT-based ISEs were calibrated against CNT-based REs, and the short-term stability of the system was tested. We demonstrate that CNT-based devices implemented on a flexible support are a very attractive platform for future wearable technology devices.

Optimized Potentiometric Assay for Non‐invasive Investigation of Skin Antioxidant Activity

“…Current parameters of interest, concerning the skin and secretion of skin glands, include pH , concentration of cations Na + , Ca 2+ , heavy metal ions ; glucose , lactate ions , chloride ions , ethanol .…”

Wearable flexible sweat sensors for healthcare monitoring: a review

“…The use of paper for substrates has also been successfully demonstrated for wearable disposable sensors, showing an improvement in sensitivity over sensors fabricated on non-porous substrates such as PI [60]. However, PI has still been preferred over PDMS due to the latter's tendency to undergo mild swelling due to ISM solution absorption [25].…”

“…Some of the most commonly measured analytes in sweat are electrolytes, such as sodium [15,17,25], potassium [3,26] and chloride [27,28]. Although sodium has been shown to be a useful marker for electrolyte imbalance [15], there is no evidence of any correlation between blood and sweat sodium [13].…”

Ultrathin Fully Printed Light‐Emitting Electrochemical Cells with Arbitrary Designs on Biocompatible Substrates

“…[1][2][3][4][5][6] Many new technologies are demanding for electronic devices that are flexible and attachable to any kind of surface and in addition are biocompatible to be installed in the direct periphery of the human body for commodity or healthcare applications. [1][2][3][4][5][6] Many new technologies are demanding for electronic devices that are flexible and attachable to any kind of surface and in addition are biocompatible to be installed in the direct periphery of the human body for commodity or healthcare applications.…”

“…Wearable and conformable electronics are among the most rapidly rising research fields in engineering and life science in recent years. [1][2][3][4][5][6] Many new technologies are demanding for electronic devices that are flexible and attachable to any kind of surface and in addition are biocompatible to be installed in the direct periphery of the human body for commodity or healthcare applications. [7] Technologic areas requesting such properties are for example the "Internet-of-things" (IOT) for which a large number of sensors and electronic devices needs to be installed in our daily life to track huge amounts of data without interfering with our general habits.…”