Structural control of mixed ionic and electronic transport in conducting polymers.

UNLABELLED: Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate), PEDOT: PSS, has been utilized for over two decades as a stable, solution-processable hole conductor. While its hole transport properties have been the subject of intense investigation, recent work has turned to PEDOT: PSS as a mixed ionic/electronic conductor in applications including bioelectronics, energy storage and management, and soft robotics. Conducting polymers can efficiently transport both holes and ions when sufficiently hydrated, however, little is known about the role of morphology on mixed conduction. Here, we show that bulk ionic and electronic mobilities are simultaneously affected by processing-induced changes in nano- and meso-scale structure in PEDOT: PSS films. We quantify domain composition, and find that domain purification on addition of dispersion co-solvents limits ion mobility, even while electronic conductivity improves. We show that an optimal morphology allows for the balanced ionic and electronic transport that is critical for prototypical mixed conductor devices. These findings may pave the way for the rational design of polymeric materials and processing routes to enhance devices reliant on mixed conduction

High-performance transistors for bioelectronics through tuning of channel thickness.

UNLABELLED: Despite recent interest in organic electrochemical transistors (OECTs), sparked by their straightforward fabrication and high performance, the fundamental mechanism behind their operation remains largely unexplored. OECTs use an electrolyte in direct contact with a polymer channel as part of their device structure. Hence, they offer facile integration with biological milieux and are currently used as amplifying transducers for bioelectronics. Ion exchange between electrolyte and channel is believed to take place in OECTs, although the extent of this process and its impact on device characteristics are still unknown. We show that the uptake of ions from an electrolyte into a film of poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate ( PEDOT: PSS) leads to a purely volumetric capacitance of 39 F/cm(3). This results in a dependence of the transconductance on channel thickness, a new degree of freedom that we exploit to demonstrate high-quality recordings of human brain rhythms. Our results bring to the forefront a transistor class in which performance can be tuned independently of device footprint and provide guidelines for the design of materials that will lead to state-of-the-art transistor performance

Chapter 13: Polymers/PEDOT Derivatives for Bioelectronics

The advancement of bioelectronics depends greatly on new material development and engineering solutions. Redox polymers are promising candidates to contribute to this advancement of biointerfacing devices. For such devices to be clinically useful, they must fulfill an assortment of requirements, including biocompatibility, stability, mechanical compliancy and the ability to effectively monitor or influence biological systems. The use of redox polymers in bioelectronic research has demonstrated a great deal of potential in satisfying these constraints. In this chapter, we consider the advantageous aspects of polymer electronics for biomedical applications including electrophysiological recording, neuromodulation, biosensor technologies and drug delivery. Particular emphasis is given to PEDOT-based systems as these have demonstrated the highest degree of bioelectronic device success to date, however, other polymers are also discussed when pertinent

Synaptic plasticity functions in an organic electrochemical transistor

Synaptic plasticity functions play a crucial role in the transmission of neural signals in the brain. Short-term plasticity is required for the transmission, encoding, and filtering of the neural signal, whereas long-term plasticity establishes more permanent changes in neural microcircuitry and thus underlies memory and learning. The realization of bioinspired circuits that can actually mimic signal processing in the brain demands the reproduction of both short- and long-term aspects of synaptic plasticity in a single device. Here, we demonstrate the implementation of neuromorphic functions similar to biological memory, such as short- to long-term memory transition, in non-volatile organic electrochemical transistors (OECTs). Depending on the training of the OECT, the device displays either short- or long-term plasticity, therefore, exhibiting non von Neumann characteristics with merged processing and storing functionalities. These results are a first step towards the implementation of organic-based neuromorphic circuits

Light sensors and opto-logic gates based on organic electrochemical transistors

In this study, we combine a photochemical cell with a transistor, forming a novel optical-to-electronic interface using OECTs with a light-sensitive gate, which can be used for photonic, optogenetic and other applications where conversion from an optical to electronic signal is key.</p

Ionic liquid gel-assisted electrodes for long-term cutaneous recordings

The integration of an ionic liquid gel on conformal electrodes is investigated for applications in long-term cutaneous recordings. Electrodes made of Au and the conducting polymer PEDOT:PSS coated with the gel show a low impedance in contact with the skin that maintains a steady value over several days, paving the way for non-invasive, long-term monitoring of human electrophysiological activity

A facile biofunctionalisation route for solution processable conducting polymer devices

For the majority of biosensors or biomedical devices, immobilization of the biorecognition element is a critical step for device function. To achieve longer lifetime devices and controllable functionalization, covalent immobilisation techniques are preferred over passive adhesion and electrostatic interactions. The rapidly emerging field of organic bioelectronics uses conducting polymers (or small molecules) as the active materials for transduction of the biological signal to an electronic one. While a number of techniques have been utilized to entrap or functionalize conducting polymers deposited by electro- or vapor phase polymerization, covalent functionalization of solution processed films, essential for realizing low cost or high throughput fabrication, has not been thoroughly investigated. In this study we show a versatile biofunctionalization technique for the solution processable conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) PEDOT:PSS, which is a commercially available material, and has a record high conductivity. Addition of poly(vinyl alcohol) (PVA) into the solution with PEDOT:PSS provides a handle for subsequent silanization with a well-characterised silane reagent, allowing for covalent linkage of biological moieties onto PEDOT:PSS films. We show homogenous and large-scale biofunctionalization with polypeptides and proteins, as well as maintenance of the biological functionalities of the proteins. In addition, no deleterious effects are noted on the electronic or ionic transport properties of the conducting polymer films due to incorporation of the PVA. This journal is © the Partner Organisations 2014

Organic Transistor Arrays Integrated with Finger-Powered Microfluidics for Multianalyte Saliva Testing.

A compact multianalyte biosensing platform is reported, composed of an organic electrochemical transistor (OECT) microarray integrated with a pumpless "finger-powered" microfluidic, for quantitative screening of glucose, lactate, and cholesterol levels. A biofunctionalization method is designed, which provides selectivity towards specific metabolites as well as minimization of any background interference. In addition, a simple method is developed to facilitate multi-analyte sensing and avoid electrical crosstalk between the different transistors by electrically isolating the individual devices. The resulting biosensing platform, verified using human samples, offers the possibility to be used in easy-to-obtain biofluids with low abundance metabolites, such as saliva. Based on our proposed method, other types of enzymatic biosensors can be integrated into the array to achieve multiplexed, noninvasive, personalized point-of-care diagnostics

Screen-printed organic electrochemical transistors for metabolite sensing

Screen-printed organic electrochemical transistors (OECTs) were tested as glucose and lactate sensors. The intrinsic amplification of the device allowed it to detect metabolites in low molecular range and validation tests were made on real human sweat. The development of an organically modified sol-gel solid electrolyte paves the way for all printed OECT-based biosensors

PEDOT:TOS with PEG: A biofunctional surface with improved electronic characteristics

Devices based on conducting polymers offer great promise for interfacing with cells. Here, we use vapour phase polymerisation to create a biofunctional composite material of the conducting polymer poly(3,4-ethylenedioxythiophene): tosylate (PEDOT:TOS) and the biologically relevant poly(ethylene glycol) (PEG). On the addition of PEG, electroactivity of the PEDOT is maintained, conductivity is increased, and its performance as the active material in a transistor is unaffected. Both direct and indirect biocompatibility tests prove that PEDOT:TOS and PEDOT:TOS:PEG are biocompatible and nontoxic to mammalian cells. A functionalised PEG (PEG(COOH)) was additionally introduced into PEDOT:TOS to showcase the potential of this material for use in applications requiring biofunctionalisation. © 2012 The Royal Society of Chemistry