High Performance Flexible Organic Electrochemical Transistors for Monitoring Cardiac Action Potential

Abstract

Flexible and transparent electronic devices possess crucial advantages over conventional silicon based systems for bioelectronic applications since they are able to adapt to nonplanar surfaces, cause less chronic immunoreactivity, and facilitate easy optical inspection. Here, organic electrochemical transistors (OECTs) are embedded in a flexible matrix of polyimide to record cardiac action potentials. The wafer-scale fabricated devices exhibit transconductances (12 mS V ) and drain-source on-to-off current ratios (≈10 ) comparable to state of the art nonflexible and superior to other reported flexible OECTs. The transfer characteristics of the devices are preserved even after experiencing extremely high bending strain and harsh crumpling. A sub-micrometer poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) layer results in a fast transport of ions between the electrolyte and the polymer channel characterized by a cut-off frequency of 1200 Hz. Excellent device performance is proved by mapping the propagation of cardiac action potentials with high signal-to-noise ratio. These results demonstrate that the electrical performance of flexible OECTs can compete with hard-material-based OECTs and thus potentially be used for in vivo applications.

Tuning Channel Architecture of Interdigitated Organic Electrochemical Transistors for Recording the Action Potentials of Electrogenic Cells

“…IDE arrays were used as source and drain electrodes for fabricating iOECTs, where the conducting polymer channel is in direct contact with the electrolyte ( Figure a). 27 individual iOECT devices are located on 1 × 1 cm 2 borofloat glass chips and spaced 200 µm center‐to‐center, similar to our previously reported flexible OECTs . Although the iOECTs possess a planar architecture, their channel dimensions can be tuned in a versatile manner by changing the number ( N f ), width ( W f ), and length of electrode fingers ( L f ), as well as the channel length ( L ch ) (Figure b).…”

“…Device Fabrication : The fabrication process, as reported previously, included optical lithography, deposition of metal, and patterning of polyimide and PEDOT:PSS. A lift‐off photoresist stack (LOR 3b, Microchem, Newton, USA and AZ nLOF 2020, MicroChemicals, Ulm, Germany) was spin‐coated on glass wafers (Borofloat, Schott, Germany) at 3000 rpm and then photolithographically patterned for source and drain electrodes using a mask aligner (MA/BA‐8, Süss MicroTec, Garching, Germany).…”

“…The resulting PEDOT:PSS thickness (115 nm) was determined by an ellipsometer (SE800, Sentech GmbH, Starnberg, Germany)). The obtained chips were encapsulated on a carrier as previously reported to match the electrical analyzing equipment. All above chemicals were obtained from Sigma (Sigma‐Aldrich, Steinheim, Germany) and used without further purification.…”

“…The resulting variation of polymer conductivity can be sensed by applying a bias between the source and drain electrode of the OECTs, which is thus operated as an amplifying transducer . Since many physiological processes are accompanied by variations of the ionic composition such as DNA hybridization, protein binding, or transmission of an action potentials, OECTs are generically suited to monitor these processes.…”

“…A crucial parameter that characterizes the signal amplification of OECTs is the transconductance ( g m ), g m = Δ I ds /Δ V gs , by converting a variation of the gate voltage originating from a biological process into a modulation of source–drain current, Δ I ds . Previously reported transconductances of OECTs (12 mS V −1 ) are superior to other electrolyte‐gated transistors, such as silicon nanowire field‐effect transistors (167 µS V −1 ), GFETs (4.2 mS V −1 ), and diamond FET arrays (90 µS V −1 ) . The transconductance of OECTs is critically dependent on the width‐to‐length ratio ( W / L ch ) of the source–drain channel and the film thickness d of conducting polymer.…”