Fully Transparent, Ultrathin Flexible Organic Electrochemical Transistors with Additive Integration for Bioelectronic Applications

Abstract

Optical transparency is highly desirable in bioelectronic sensors because it enables multimodal optical assessment during electronic sensing. Ultrathin (<5 µm) organic electrochemical transistors (OECTs) can be potentially used as a highly efficient bioelectronic transducer because they demonstrate high transconductance during low‐voltage operation and close conformability to biological tissues. However, the fabrication of fully transparent ultrathin OECTs remains a challenge owing to the harsh etching processes of nanomaterials. In this study, fully transparent, ultrathin, and flexible OECTs are developed using additive integration processes of selective‐wetting deposition and thermally bonded lamination. These processes are compatible with Ag nanowire electrodes and conducting polymer channels and realize unprecedented flexible OECTs with high visible transmittance (>90%) and high transconductance (≈1 mS) in low‐voltage operations (<0.6 V). Further, electroencephalogram acquisition and nitrate ion sensing are demonstrated in addition to the compatibility of simultaneous assessments of optical blood flowmetry when the transparent OECTs are worn, owing to the transparency. These feasibility demonstrations show promise in contributing to human stress monitoring in bioelectronics.

A High‐Resolution, Transparent, and Stretchable Polymer Conductor for Wearable Sensor Arrays

“…The aesthetic impression to the user can determine the adherence of wearable devices, with transparent devices minimally influencing the original appearance. Furthermore, transparency allows us to integrate optical healthcare sensors to add multimodality [3] or displays for the indication of obtained signals from the sensors. [4] For the realization of stretchable and transparent sensor arrays, it is important to develop high-resolution patternable, transparent, and stretchable conductors.…”

Neural-inspired artificial synapses based on low-voltage operated organic electrochemical transistors

“…In stretchable electronics, flexible electrodes can be fabricated on a thin metal coating on a flexible substrate or by adding conductive fillers. 126,127 The most reported stretchable conductors are silver nanowires (AgNWs), 128 Ag epoxy, 129 copper nanowires (CuNWs), 130 CNT, 131 graphene, [132][133][134] and fractal Ag nanostructures 135 included in any elastomer. Conductive polymers and their composites can also serve as flexible electrodes.…”

Recent Progress on Transparent Microelectrode-Based Soft Bioelectronic Devices for Neuroscience and Cardiac Research

“…PEDOT:PSS was prepared by spin coating and patterned by 4h). 126 The Ag NWs source/ drain electrodes and 180 nm thick PEDOT:PSS active layer were patterned on a 1 μm thick parylene C substrate via selective wetting deposition using rod coating with a high resolution down to 20 μm. The encapsulation parylene was bonded via the thermal lamination.…”

“…(Right) Transconductance characteristics with and without the white LED illumination. Reproduced from ref . Copyright 2023, Wiley.…”

“…The optogenetically evoked ECoG signals by a 473 nm laser beam from the transparent OECTs exhibited twice the amplitude (700 μV) with minimized reflections of laser stimulation compared to reference nontransparent OECTs. More recently, Takemoto et al developed another flexible and transparent OECT array with Ag NWs electrodes and a PEDOT:PSS channel (Figure h) . The Ag NWs source/drain electrodes and 180 nm thick PEDOT:PSS active layer were patterned on a 1 μm thick parylene C substrate via selective wetting deposition using rod coating with a high resolution down to 20 μm.…”