PEDOT:PSS Paving The Future of Remote Healthcare

2025/02/10

The Institute of Scientific and Industrial Research, Osaka University,
Associate Professor　Teppei Araki

Abstract

The integration of wireless communication and flexible electronics in remote healthcare is expected to play a key role in next-generation personalized medicine by enabling real-time physiological monitoring. In particular, flexible electronics exhibit high biocompatibility, making them well suited for long-term physiological monitoring. The efficient AI processing of large-scale personal health data, combined with appropriate medical support, facilitates the realization of user-oriented remote healthcare. This article highlights an advanced remote healthcare technology enabled by PEDOT:PSS-based flexible bioelectrodes and organic electrochemical transistors (OECT) that securely adhere to the body and provide stable, long-term physiological monitoring. PEDOT:PSS-based flexible devices not only support multimodal sensing of various physiological signals, including brain activity, cardiac function, muscular contractions, oxygen saturation, blood circulation, and ionic concentrations in biological metabolites, but also contribute to a comprehensive physiological state prediction. Advancements in PEDOT:PSS, from material development to applications, are making sophisticated health tracking an essential part of daily life, thereby accelerating the evolution of personalized medicine.

Main text

1. Introduction

Flexible electronics is a field focused on developing electronic device technologies that exhibit durability against mechanical deformations, such as bending and twisting. This technology enables applications to curved surfaces and dynamic measurement targets, which are difficult to achieve using conventional rigid devices. In particular, research aimed at developing electronic devices with high stretchability, similar to rubber, is referred to as stretchable electronics in a narrow sense. In a broader sense, flexible electronics possess mechanical flexibility, allowing them to conform to the curves and movements of the human body. This reduces discomfort when worn, and enables long-term use. Furthermore, incorporating optical transparency facilitates the development of unobtrusive electronic devices, leading to a society in which electronics are naturally integrated into the human body and daily life. In the future, flexible electronics are expected to be applied in a wide range of fields, including healthcare, robotics, wearable devices, civil engineering, architecture, and agriculture.
Recent advancements in wireless communication technology and AI-driven analytical techniques have led to a global surge in research and development focused on the application of advanced electronics to remote healthcare. As medical digitalization progresses, the healthcare landscape is expected to undergo significant transformation. One such transformation is personalized healthcare (precision medicine), which aims to provide optimized medical care tailored to an individual's health condition. In recent years, the development of compact and lightweight wearable devices capable of acquiring physiological signals, such as brain waves, electrocardiograms, pulse rates, and blood-oxygen saturation, has accelerated. In parallel, research efforts have expanded to elucidate the relationships between daily activities and physiological functions as well as to advance methods for early disease identification. However, challenges such as fatigue, discomfort due to prolonged wear, and signal noise persist. In the field of biosignal measurement, probes capable of accurately capturing microvolt (µV)-level electrical potential changes are essential under long-term monitoring.
PEDOT:PSS, a conductive polymer, offers high conductivity, flexibility, biocompatibility, and compatibility with printing processes, making it widely applicable in flexible bioelectrodes and organic electrochemical transistors (OECT). In practice, advancements in the design of nanomaterials utilizing PEDOT:PSS, along with the optimization of nanonetwork structures, have not only enabled the development of low-noise, high-sensitivity characteristics essential for biosignal measurement but have also driven the creation of multifunctional probes with long-term stability, stretchability, and transparency. PEDOT:PSS continues to attract significant attention as a key flexible material for future remote healthcare applications.
Chapter 2 focuses on the bioelectrodes and systems for remote measurements. Chapter 3 examines micro-bioelectrodes and their applications in OECT. The final chapter, Chapter 4, presents the conclusions of this study.

2. Transparent e-skin: stretchable dry-type bioelectrodes and low-noise remote measurement

Notably, this elastomer network contributes to achieving flexibility comparable to that of human skin (Young’s modulus: 7 kPa–0.5 MPa), high optical transparency (over 85%), and exceptional stretchability (maximum strain: 1126–1537%). A sheet-type sensor system, connected to a compact wireless module, leveraged the superior electrical conductivity of dry-type bioelectrode to achieve an ultra-low noise floor (approximately 0.14 µV), comparable to medical-grade materials. When attached to the forehead to acquire electroencephalography (EEG), subtle alpha wave signals were successfully measured during eye closure (frequency: 8–13 Hz; amplitude: approximately 1.8–13.9 µV). Furthermore, even during sleep, where low-frequency recording down to around 0.1 Hz is required, this system enabled high-precision sleep stage classification through EEG measurement and AI analysis. The biocompatibility of dry-type bioelectrode was confirmed through ISO 10993 testing and a 24-hour skin patch test. As a result, it was demonstrated that both EEG and other electrophysiological signals, such as electrocardiography (ECG) and electromyography (EMG), were remotely measured with low noise and high safety.
In addition to overcoming the limitations of conventional wet-type bioelectrodes, the dry-type bioelectrode is seamlessly integrated with camera-based photoplethysmography (PPG) without obstructing the optical path because of its transparency. This feature enables remote monitoring of subtle cardiovascular changes and blood oxygen saturation associated with stress conditions. Owing to its multifunctionality and high sensitivity in biosignal detection, the dry-type bioelectrode shows great potential as a next-generation transparent e-skin that integrates with the human body.
The evolution of e-skin is ongoing, with research and development efforts focused on various technologies, including bioelectrodes and remote healthcare devices with enhanced usability [1–6], environment-friendly devices utilizing nanocellulose as a natural material [7], self-sustaining devices that harness ambient energy[8], and edge AI devices equipped with memristors [9] (Figure 2).

Figure 2. Image on evolution of flexible electronics. Attribution 4.0 International (CC BY 4.0), Reprinted with permission of [9] from Advanced Materials.

3. Flexible, transparent micro-bioelectrodes with signal amplification function

※ This chapter cites data and other information from Reference [2,3].
In conventional transparent electrodes, metal oxides, such as indium tin oxide (ITO), have been widely applied to various optical devices, including displays and solar cells, owing to their excellent transparency and electrical properties. However, the high brittleness of metal oxides limits their applications in flexible devices. In response to this challenge, recent studies have proposed flexible transparent electrodes and transistors utilizing various nanomaterials, including one-dimensional inorganic nanomaterials such as metal nanowires, carbon nanomaterials such as carbon nanotubes, conductive polymers such as PEDOT:PSS, and two-dimensional layered compounds such as MXene. Among these, silver nanowires (AgNWs), which can form highly conductive nanostructures, and PEDOT:PSS, which allows tunable electrical conductivity through electrochemical doping and dedoping, are particularly noteworthy as promising materials for enabling transparent and flexible components in applications such as biosensors, optoelectronic devices, wearable devices, implantable devices, and human-machine interfaces.
For device development utilizing AgNW and PEDOT:PSS, it is advantageous to employ additive manufacturing techniques such as high-resolution printing processes and thermal lamination. The primary benefit of additive techniques is that, in comparison to conventional etching processes used in electronics manufacturing, they constitute a mild fabrication method that minimizes the chemical effects on organic substrates and inorganic nanomaterials. Through the repeated patterning and layering of AgNW, PEDOT:PSS, and insulators via additive techniques, it is feasible to fabricate fully transparent, ultrathin, and flexible micro bioelectrodes and transistors.
Using high-resolution printing processes, AgNW-based electrodes formed on polymer substrates with thicknesses of approximately 1–10 µm exhibited multifunctional and high-performance characteristics, including excellent conductivity (~25 Ω/sq), high optical transmittance (96–99%), applicability to fine patterning (minimum 20 µm), and high bending durability (bending radius: 0.8 mm). Moreover, AgNW/Au nanowires, fabricated by electroless plating of a few nanometers of gold (Au) onto the AgNW surface, maintained the high conductivity and transparency of AgNW, and demonstrated improved stretchability (~100% strain) and enhanced corrosion resistance (~20 times)(Figure 3). For further improvement of the stretch durability, high-intensity pulsed light irradiation, which can be sintered in 1 ms, is also effective. The AgNW/Au-based electrode with high durability obtained enables long-term measurement of biological signals, and the electrical characteristics during this period are also found to be less deteriorated.

Figure 3. AgNW/Au-based electrode. a) Cross-sectional AgNW/Au image obtained using transmission electron microscopy. b) Schematic of AgNW/Au after photonic sintering. c) Change in resistance (measured resistance divided by resistance before the test) under mechanical tensile strain for pristine and photonically sintered AgNW/Au. Recovery to 1.4–4.5-fold variation is observed after 100 cycles. Attribution 4.0 International (CC BY 4.0), Reprinted with permission of [1] from Advanced Materials Technologies.

Micro-bioelectrodes combining AgNW-based electrodes with PEDOT:PSS maintain high conductivity, optical transparency, and mechanical flexibility. In comparison to standalone AgNW-based microelectrodes, the primary advantage of this composite electrode is the characteristic electrochemical properties of PEDOT:PSS, which result in an approximately tenfold reduction in contact impedance in electrolytes. As a result, high signal quality has been demonstrated in biosensing applications such as plant potential and EEG.
The transistor is a three-terminal device (S/D/G), wherein AgNW-based microelectrodes are pre-formed as the source (S) and drain (D), followed by the deposition of an active layer (channel) between the source and drain, and the construction of an AgNW-based gate (G) on top of the channel. For instance, by utilizing PEDOT:PSS as the channel material, an organic electrochemical transistor (OECT) can be realized (Figure 4), which exhibits outstanding properties, such as high optical transparency (>90%), low operating voltage (<0.6V), and high transconductance related to signal amplification (~1 mS. The current gain is 100 or more. The voltage gain for a load resistance type inverter is around 6.).

4. Summary

A remote measurement system integrating flexible bioelectrodes and transistors has the potential to serve as an innovative platform for real-time, wireless home healthcare monitoring. Flexible bioelectrodes and transistors developed using AgNW that synergizes with PEDOT:PSS function as key components of ultrathin sheet-type sensors with a thickness of approximately 1–10 µm. These sheet-type sensors exhibit both stretchability and transparency, enabling them to adhere to the skin without causing discomfort while facilitating stable measurement of a wide range of micro-signals, including EEG, ECG, EMG, pulse waves, blood flow, blood oxygen saturation, and nitrate ion concentration. Furthermore, a sensor system combining sheet-type sensors with compact and lightweight wireless measurement devices has the potential to transform conventional large-scale medical equipment into palm-sized medical devices. Notably, the capability of achieving ultra-low-noise signal measurement even during continuous monitoring suggests the feasibility of implementing highly precise feedback systems. Consequently, in the near future, remote healthcare is anticipated to enable the realization of highly advanced personalized medicine optimized for individual patients.

References
[1] Teppei Araki, Shusuke Yoshimoto, Takafumi Uemura, Aiko Miyazaki, Naoko Kurihira, Yuko Kasai, Yoshiko Harada, Toshikazu Nezu, Hirokazu Iida, Junko Sandbrook, Shintaro Izumi, and Tsuyoshi Sekitani.
"Skin-Like Transparent Sensor Sheet for Remote Healthcare Using Electroencephalography and Photoplethysmography."
Advanced Materials Technologies, vol. 7, no. 11, 202200362, 2022
DOI: 10.1002/admt.202200362
[2] Ashuya Takemoto, Teppei Araki, Takafumi Uemura, Yuki Noda, Shusuke Yoshimoto, Shintaro Izumi, Shuichi Tsuruta, and Tsuyoshi Sekitani.
"Printable Transparent Microelectrodes toward Mechanically and Visually Imperceptible Electronics."
Advanced Intelligent Systems, vol. 2, no. 11, 202000093, 2020
DOI: 10.1002/aisy.202000093
[3] Ashuya Takemoto, Teppei Araki, Kazuya Nishimura, Mihoko Akiyama, Takafumi Uemura, Kazuki Kiriyama, Johan M. Koot, Yuko Kasai, Naoko Kurihira, Shuto Osaki, Shin-ichi Wakida, Jaap M.J. den Toonder, and Tsuyoshi Sekitani.
"Fully Transparent, Ultrathin Flexible Organic Electrochemical Transistors with Additive Integration for Bioelectronic Applications."
Advanced Science, vol. 10, no. 2, 202204746, 2022
DOI: 10.1002/advs.202204746
[4] Teppei Araki, Takafumi Uemura, Shusuke Yoshimoto, Ashuya Takemoto, Yuki Noda, Shintaro Izumi, and Tsuyoshi Sekitani.
"Wireless Monitoring Using a Stretchable and Transparent Sensor Sheet Containing Metal Nanowires."
Advanced Materials, vol. 32, no. 15, 1902684, 2019
DOI: 10.1002/adma.201902684
[5] Teppei Araki, Fumiaki Yoshida, Takafumi Uemura, Yuki Noda, Shusuke Yoshimoto, Taro Kaiju, Takafumi Suzuki, Hiroki Hamanaka, Kousuke Baba, Hideki Hayakawa, Taiki Yabumoto, Hideki Mochizuki, Shingo Kobayashi, Masaru Tanaka, Masayuki Hirata, and Tsuyoshi Sekitani.
"Long-Term Implantable, Flexible, and Transparent Neural Interface Based on Ag/Au Core–Shell Nanowires."
Advanced Healthcare Materials, vol. 8, no. 10, 1900130, 2020
DOI: 10.1002/adhm.201900130
[6] Teppei Araki, Lukas M Bongartz, Taro Kaiju, Ashuya Takemoto, Shuichi Tsuruta, Takafumi Uemura, and Tsuyoshi Sekitani
"Flexible Neural Interfaces for Brain Implants—The Pursuit of Thinness and High Density."
Flexible and Printed Electronics, vol. 5, 043002, 2020
DOI: 10.1088/2058-8585/abc3ca
[7] Yintong Huang, Teppei Araki, Naoko Kurihira, Takaaki Kasuga, Tsuyoshi Sekitani, Masaya Nogi, and Hirotaka Koga.
"Skin-Adhesive, -Breathable, and -Compatible Nanopaper Electronics for Harmonious On-Skin Electrophysiological Monitoring."
Advanced Materials Interfaces, vol. 10, no. 13, 2202263, 2023
DOI: 10.1002/admi.202202263
[8] Andreas Petritz, Esther Karner-Petritz, Takafumi Uemura, Philipp Schäffner, Teppei Araki, Barbara Stadlober, and Tsuyoshi Sekitani.
"Imperceptible Energy Harvesting Device and Biomedical Sensor Based on Ultraflexible Ferroelectric Transducers and Organic Diodes."
Nature Communications, vol. 12, 2399, 2021
DOI: 10.1038/s41467-021-22663-6
[9] Teppei Araki, Kou Li, Daichi Suzuki, Takaaki Abe, Rei Kawabata, Takafumi Uemura, Shintaro Izumi, Shuichi Tsuruta, Nao Terasaki, Yukio Kawano, and Tsuyoshi Sekitani.
"Broadband Photodetectors and Imagers in Stretchable Electronics Packaging."
Advanced Materials, vol. 36, 202304048, 2023
DOI: 10.1002/adma.202304048