Roughness-induced energetic disorder at the metal/organic interface

The amplitude of the roughness-induced energetic disorder at the metal/organic interface is calculated. It was found that for moderately rough electrodes, the correction to the electrostatic image potential at the charge location is small. For this reason, roughness-induced energetic disorder cannot noticeably affect charge carrier injection, contrary to the recent reports.This work was supported by the ISTC Grant No. 2207 and RFBR grants 05-03-33206 and 03-03-33067. The research described in this publication was made possible in part by Award No. RE2-2524-MO-03 of the U.S. Civilian Research & Development Foundation for the Independent States of the Former Soviet Union (CRDF)

Stability of PEDOT:PSS-Coated Gold Electrodes in Cell Culture Conditions

Poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) is widely used as a coating on microelectrode arrays in order to reduce impedance for both in vitro and in vivo electrophysiology. In many applications, electrode performance of months to years is desired; yet, there are few studies to date that examine the long-term stability of conducting polymers and their devices. Here, the stability of PEDOT:PSS microelectrodes is examined over a period of four months in cell culture media enriched with fetal bovine serum. The electrochemical impedance remains constant for most electrodes throughout the study, and only small changes in the structure of functional electrodes are observed at the end of the test. The results demonstrate that PEDOT:PSS electrodes show adequate stability for a variety of in vitro electrophysiology applications in toxicology, drug development, tissue engineering, and fundamental studies of electrically active cells and tissues.A.L.R. acknowledges support from the Whitaker International Scholars Program and the European Commission’s Horizon 2020 Marie Sklodowska-Curie Individual Fellowship BRAIN CAMO (No. 797506). G.D. acknowledges support from the European Commission through the project of OrgBIO-ITN 607896

Silicon-Bridged donor-acceptor compounds: synthesis and nonlinear optical properties

This thesis describes the synthesis and the spectroscopic and nonlinear optical characterization of a large series of donor- and acceptor-substituted diphenylsilanes with the structure DPh-(SiMez).-PhA and fragments thereof. Nonlinear optics (NLO) deals with the interaction of electromagnetic fields (light) with matter so as to generate new electromagnetic fields altered from the incident field with respect to phase, frequency, amplitude or other propagation characteristics. One of the applications involving nonlinear optical phenomena is frequency doubling of near infrared laser light (frequency a) by a nonlinear optical material into blue light. ... Zie: Summery

A Disposable paper breathalyzer with an alcohol sensing organic electrochemical transistor.

UNLABELLED: Breathalyzers estimate Blood Alcohol Content (BAC) from the concentration of ethanol in the breath. Breathalyzers are easy to use but are limited either by their high price and by environmental concerns, or by a short lifetime and the need for continuous recalibration. Here, we demonstrate a proof-of-concept disposable breathalyzer using an organic electrochemical transistor (OECT) modified with alcohol dehydrogenase (ADH) as the sensor. The OECT is made with the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT: PSS), and is printed on paper. ADH and its cofactor nicotinamide adenine dinucleotide (NAD(+)) are immobilized onto the OECT with an electrolyte gel. When the OECT-breathalyzer is exposed to ethanol vapor, the enzymatic reaction of ADH and ethanol transforms NAD(+) into NADH, which causes a decrease in the OECT source drain current. In this fashion, the OECT-breathalyzer easily detects ethanol in the breath equivalent to BAC from 0.01% to 0.2%. The use of a printed OECT may contribute to the development of breathalyzers that are disposable, ecofriendly, and integrated with wearable devices for real-time BAC monitoring

Direct patterning of organic conductors on knitted textiles for long-term electrocardiography.

Wearable sensors are receiving a great deal of attention as they offer the potential to become a key technological tool for healthcare. In order for this potential to come to fruition, new electroactive materials endowing high performance need to be integrated with textiles. Here we present a simple and reliable technique that allows the patterning of conducting polymers on textiles. Electrodes fabricated using this technique showed a low impedance contact with human skin, were able to record high quality electrocardiograms at rest, and determine heart rate even when the wearer was in motion. This work paves the way towards imperceptible electrophysiology sensors for human health monitoring

Hybrid 3D/Inkjet-Printed Organic Neuromorphic Transistors

Organic electrochemical transistors (OECTs) are proving essential in bioelectronics and printed electronics applications, with their simple structure, ease of tunability, biocompatibility and suitability for different routes to fabrication. OECTs are also being explored as neuromorphic devices, where they emulate characteristics of biological neural networks through co-location of information storage and processing on the same unit, overcoming the von Neumann performance bottleneck. To achieve the long-term vision of translating to inexpensive, low-power computational devices, fabrication needs to be feasible with adaptable, scalable digital techniques. Here we show a hybrid direct-write additive manufacturing approach to fabricating OECTs. We combine 3D printing of commercially available printing filament to deliver conducting and insulating layers, with inkjet printing of a semi-conducting thin films to create OECTs. These printed OECTs show depletion mode operation paired-pulse depression behaviour and evidence of adaptation to support their translation to neuromorphic devices. These results show that a hybrid of accessible and design-flexible AM techniques can be used to rapidly fabricate devices that exhibit good OECT and neuromorphic performances.EP/L016567/

Using white noise to gate organic transistors for dynamic monitoring of cultured cell layers.

Impedance sensing of biological systems allows for monitoring of cell and tissue properties, including cell-substrate attachment, layer confluence, and the "tightness" of an epithelial tissue. These properties are critical for electrical detection of tissue health and viability in applications such as toxicological screening. Organic transistors based on conducting polymers offer a promising route to efficiently transduce ionic currents to attain high quality impedance spectra, but collection of complete impedance spectra can be time consuming (minutes). By applying uniform white noise at the gate of an organic electrochemical transistor (OECT), and measuring the resulting current noise, we are able to dynamically monitor the impedance and thus integrity of cultured epithelial monolayers. We show that noise sourcing can be used to track rapid monolayer disruption due to compounds which interfere with dynamic polymerization events crucial for maintaining cytoskeletal integrity, and to resolve sub-second alterations to the monolayer integrity

A DC Model for Organic Electrochemical Transistors and Analysis of Their Performance as Voltage Amplifiers

Organic electrochemical transistors (OECTs) have received significant attention especially in biomedical applications. Despite many efforts on modeling these transistors, simulating OECT-based circuits is still a challenge due to the absence of accurate mathematical models. In this paper a DC model for p-type depletion-mode OECTs is proposed that more closely mimics their characteristics compared to the Bernards-Malliaras (B-M) model. Although OECTs are mostly used as transconductance amplifiers, their use as voltage amplifiers is investigated here with measurements at various drain-source voltages. Compared to the B-M model, the proposed model has better matching up to 3.6% between simulations and measurements of the analyzed transistors

Effect of channel thickness on noise in organic electrochemical transistors

Organic electrochemical transistors (OECTs) have been widely used as transducers in electrophysiology and other biosensing applications. Their identifying characteristic is a transconductance that increases with channel thickness, and this provides a facile mechanism to achieve high signal amplification. However, little is known about their noise behavior. Here, we investigate noise and extract metrics for the signal-to-noise ratio and limit of detection in OECTs with different channel thicknesses. These metrics are shown to improve as the channel thickness increases, demonstrating that OECTs can be easily optimized to show not only high amplification, but also low noise.</jats:p

Impact of contact overlap on transconductance and noise in organic electrochemical transistors

Abstract Organic electrochemical transistors (OECTs) from poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) are used as amplifying transducers for bioelectronics. Although the impact on performance of device geometry parameters such as channel area and thickness has been widely explored, the overlap between the semiconductor film and the source and drain contacts has not been considered. Here we vary this overlap and explore its impact on transconductance and noise. We show that increasing contact overlap does not alter the magnitude of the steady-state transconductance but it does decreases the cut-off frequency. Noise was found to be independent of contact overlap and to vary according to the charge noise model. The results show that high-quality contacts can be established in PEDOT:PSS OECTs with minimal overlap.</jats:p