Roll-to-roll fabrication of silver/silver chloride coated yarns for dry electrodes and applications in biosignal monitoring.

This work presents a continuous roll-to-roll electrochemical coating system for producing silver/silver chloride (Ag/AgCl)-coated yarns, and their application in e-textile electrodes for biosignal monitoring. Ag/AgCl is one of the most preferred electrode materials as an interface between the conductive backbone of an electrode and skin. E-textile Ag/AgCl-coated multi-filament nylon yarns offer stable, flexible, and breathable alternatives to standard rigid or flexible film-based Ag/AgCl electrodes. The developed system allows for highly controlled process parameters to achieve stable and uniform AgCl film deposition on Ag-coated nylon yarns. The electrical, electrochemical properties, and morphology of the coated yarns were characterized. Dry electrodes were fabricated and could measure electrocardiogram (ECG) signals with comparable performance to standard gel electrodes. Ag/AgCl e-textile electrodes demonstrated high stability, with low average polarization potential (1.22 mV/min) compared with Ag-coated electrodes (3.79 mV/min), low impedance (below 2 MΩ, 0.1-150 Hz), and are excellent candidates for heart rate detection and monitoring.

Screen-Printed Textile-Based Electrochemical Biosensor for Noninvasive Monitoring of Glucose in Sweat.

Wearable sweat biosensors for noninvasive monitoring of health parameters have attracted significant attention. Having these biosensors embedded in textile substrates can provide a convenient experience due to their soft and flexible nature that conforms to the skin, creating good contact for long-term use. These biosensors can be easily integrated with everyday clothing by using textile fabrication processes to enhance affordable and scalable manufacturing. Herein, a flexible electrochemical glucose sensor that can be screen-printed onto a textile substrate has been demonstrated. The screen-printed textile-based glucose biosensor achieved a linear response in the range of 20-1000 µM of glucose concentration and high sensitivity (18.41 µA mM-1 cm-2, R2 = 0.996). In addition, the biosensors show high selectivity toward glucose among other interfering analytes and excellent stability over 30 days of storage. The developed textile-based biosensor can serve as a platform for monitoring bio analytes in sweat, and it is expected to impact the next generation of wearable devices.

Breathable Dry Silver/Silver Chloride Electronic Textile Electrodes for Electrodermal Activity Monitoring.

The focus of this study is to design and integrate silver/silver chloride (Ag/AgCl) electronic textile (e-textile) electrodes into different textile substrates to evaluate their ability to monitor electrodermal activity (EDA). Ag/AgCl e-textiles were stitched into woven textiles of cotton, nylon, and polyester to function as EDA monitoring electrodes. EDA stimulus responses detected by dry e-textile electrodes at various locations on the hand were compared to the EDA signals collected by dry solid Ag/AgCl electrodes. 4-h EDA data with e-textile and clinically conventional rigid electrodes were compared in relation to skin surface temperature. The woven cotton textile substrate with e-textile electrodes (0.12 cm² surface area, 0.40 cm distance) was the optimal material to detect the EDA stimulus responses with the highest average Pearson correlation coefficient of 0.913 ± 0.041 when placed on the distal phalanx of the middle finger. In addition, differences with EDA waveforms recorded on various fingers were observed. Trends of long-term measurements showed that skin surface temperature affected EDA signals recorded by non-breathable electrodes more than when e-textile electrodes were used. The effective design criteria outlined for e-textile electrodes can promote the development of comfortable and unobtrusive EDA monitoring systems, which can help improve our knowledge of the human neurological system.

Light-soaking free organic photovoltaic devices with sol-gel deposited ZnO and AZO electron transport layers.

This paper investigates light-soaking effects in inverted organic photovoltaic (OPV) devices with zinc oxide (ZnO) and aluminum doped ZnO (AZO) electron transport layers (ETL), which is important for the development of low-cost and stable solar cells. The samples demonstrated high solar harvesting properties with power conversion efficiency up to 3.9%. Air-stability tests of up to 150 days were performed on devices with different Al doping levels. The devices maintained higher than 60% of the initial PCE after 50 days of open-air exposure. The light-soaking mechanism was investigated with experiments and simulations and shown to be eliminated when the Al fraction of the AZO is higher than 4%. The simulated band diagram of the OPV devices indicates that the low carrier density in the ZnO layer by virtue of depletion is the main reason of the light-soaking effect. Doping the ZnO layer as well as exposing the devices under UV irradiation will introduce additional free carriers into the ETL and reduce the width of the depletion region at both sides of the ETL.

Effects of Flexible Dry Electrode Design on Electrodermal Activity Stimulus Response Detection.

OBJECTIVE: The focus of this research is to evaluate the effects of design parameters including surface area, distance between and geometry of dry flexible electrodes on electrodermal activity (EDA) stimulus response detection. METHODS: EDA is a result of the autonomic nervous system being stimulated, which causes sweat and changes the electrical characteristics of the skin. Standard silver/silver chloride (Ag/AgCl) EDA electrodes are rigid and lack conformability in contact with skin. In this study, flexible dry Ag/AgCl EDA electrodes were fabricated on a compliant substrate, used to monitor EDA stimulus responses and compared to results simultaneously collected by rigid dry Ag/AgCl electrodes. RESULTS: A repeatable fabrication process for flexible Ag/AgCl electrodes has been established. Surface area, distance between and geometry of electrodes are shown to affect the detectability of the EDA response and the minimum number of sweat glands to be covered by the electrodes has been estimated at 140, or more, in order to maintain functionality. The optimal flexible EDA electrode is a serpentine design with a 0.15 cm2 surface area and a 0.20 cm distance with an average Pearson correlation coefficient of . CONCLUSION: Fabrication of flexible electrodes is described and an understanding of the effects of electrode designs on the EDA stimulus response detection has been established and is potentially related to the coverage of sweat glands. SIGNIFICANCE: This work presents a novel systematic approach to understand the effects of electrode designs on monitoring EDA which is of importance for the design of wearable EDA monitoring devices.