Transistors with tunable transconductance allow high-quality recordings of human brain rhythms.

Information processing in the brain takes place in a network of neurons that are connected with each other by an immense number of synapses. At the same time, neurons are immersed in a common electrochemical environment, and global parameters such as concentrations of various hormones regulate the overall network function. This computational paradigm of global regulation, also known as homeoplasticity, has important implications in the overall behaviour of large neural ensembles and is barely addressed in neuromorphic device architectures. Here, we demonstrate the global control of an array of organic devices based on poly(3,4ethylenedioxythiophene):poly(styrene sulf) that are immersed in an electrolyte, a behaviour that resembles homeoplasticity phenomena of the neural environment. We use this effect to produce behaviour that is reminiscent of the coupling between local activity and global oscillations in the biological neural networks. We further show that the electrolyte establishes complex connections between individual devices, and leverage these connections to implement coincidence detection. These results demonstrate that electrolyte gating offers significant advantages for the realization of networks of neuromorphic devices of higher complexity and with minimal hardwired connectivity.

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Ions are ubiquitous biological regulators playing a key role for vital processes in animals and plants. The combined detection of ion concentration and real-time monitoring of small variations with respect to the resting conditions is a multiscale functionality providing important information on health states. This multiscale functionality is still an open challenge for current ion sensing approaches. Here we show multiscale real-time and high-sensitivity ion detection with complementary organic electrochemical transistors amplifiers. The ion-sensing amplifier integrates in the same device both selective ion-to-electron transduction and local signal amplification demonstrating a sensitivity larger than 2300 mV V −1 dec −1 , which overcomes the fundamental limit. It provides both ion detection over a range of five orders of magnitude and real-time monitoring of variations two orders of magnitude lower than the detected concentration, viz. multiscale ion detection. The approach is generally applicable to several transistor technologies and opens opportunities for multifunctional enhanced bioelectronics.

We have examined the electrochemical impedance spectroscopy (EIS) of PEDOT:PSS‐coated gold electrodes in various electrolytes as a function of temporal frequency (from 0.1 to 104 Hz) by using a custom‐designed microfabricated substrate. The electrode areas were systematically varied over a broad range in nominal size from 10×10 μm (100 μm2) to 500×500 μm (2.5×105 μm2). Comparisons were made between spin‐cast PEDOT:PSS crosslinked with GOPS and electrochemically deposited PEDOT:PSS films with similar thicknesses. The impedance spectra of the PEDOT:PSS‐coated electrodes with various sizes could all be reasonably well described by a two‐element equivalent circuit model with a solution resistance Rs and a film capacitance C. These two parameters together define a characteristic temporal frequency fc=1/(2πRsC). By normalizing the impedance with respect to Rs (Zn=|Z|/Rs) and the frequency with respect to fc (fn=f/fc), we found that all of the experimental Bode curves could be collapsed onto a single master plot of Zn vs. fn. In addition, analytical formulas that allow the estimation of the film impedance magnitude |Z| and phase ϕ were derived and experimentally validated. These results are of fundamental interest and are also anticipated to be important for the design, characterization, and optimization of conjugated polymer films for interfacing biomedical devices with living tissue.

Neuromorphic devices offer promising computational paradigms that transcend the limitations of conventional technologies. A prominent example, inspired by the workings of the brain, is spatiotemporal information processing. Here we demonstrate orientation selectivity, a spatiotemporal processing function of the visual cortex, using a poly(3,4ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) organic electrochemical transistor with multiple gates. Spatially distributed inputs on a gate electrode array are found to correlate with the output of the transistor, leading to the ability to discriminate between different stimuli orientations. The demonstration of spatiotemporal processing in an organic electronic device paves the way for neuromorphic devices with new form factors and a facile interface with biology.

A robot learns to follow a path to exit a maze through sensorimotor learning that is induced by an organic neuromorphic circuit.

The conductivity of poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) can be strongly enhanced by treatment with high boiling solvents as dimethyl sulfoxide (DMSO). The effect of various DMSO solvent treatment methods on the performance of organic electrochemical transistors (OECTs) based on PEDOT:PSS is studied. The treatments include mixing PEDOT:PSS with DMSO before film deposition, exposing a deposited PEDOT:PSS film to a saturated DMSO vapor, and dipping a PEDOT:PSS film in a DMSO bath. Compared to dry PEDOT:PSS, operating in the OECT configuration causes a significant reduction of its conductivity for all treatments, due to the swelling of PEDOT:PSS by the direct contact of the conductive channel with the electrolyte. The dipping method gives rise to the highest OECT performance, reflected in the highest on/off ratio and transconductance. The improved conductivity and device performance after dipping arise from an enhanced charge carrier mobility due to enhanced structural order.