Neuromorphic device architectures with global connectivity through electrolyte gating.

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

Efficient Gating of Organic Electrochemical Transistors with In-Plane Gate Electrodes

AbstractOrganic electrochemical transistors (OECTs) are electrolyte‐gated transistors, employing an electrolyte between their gate and channel instead of an insulating layer. For efficient gating, non‐polarizable electrodes, for example, Ag/AgCl, are typically used but unfortunately, this simple approach limits the options for multiple gate integration. Patterned polarizable Au gates on the other hand, show strongly reduced gating due to a large voltage drop at the gate/electrolyte interface. Here, an alternative, simple yet effective method for efficient OECT gating by scalable in‐plane gate electrodes, is demonstrated. The fact that poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) exhibits a volumetric capacitance in an electrolyte is made use of. As a result, the capacitance of PEDOT:PSS‐based gates can be strongly enhanced by increasing their thickness, thereby reducing the voltage loss at the gate/electrolyte interface. By combining spin coating and electrodeposition, planar electrodes of various thicknesses are created on a multi‐gated OECT chip and their effect on the gating efficiency, examined. It is shown that the gating performed by an in‐plane PEDOT:PSS electrode can be tuned to be comparable to the one obtained by a Ag/AgCl electrode. Overall, the realization of efficient gating with in‐plane electrodes paves the way toward integration of OECT‐based biosensors and "organ‐on‐a‐chip" platforms

Orientation selectivity in a multi-gated organic electrochemical transistor.

UNLABELLED: 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

Current-Driven Organic Electrochemical Transistors for Monitoring Cell Layer Integrity with Enhanced Sensitivity

AbstractIn this progress report an overview is given on the use of the organic electrochemical transistor (OECT) as a biosensor for impedance sensing of cell layers. The transient OECT current can be used to detect changes in the impedance of the cell layer, as shown by Jimison et al. To circumvent the application of a high gate bias and preventing electrolysis of the electrolyte, in case of small impedance variations, an alternative measuring technique based on an OECT in a current‐driven configuration is developed. The ion‐sensitivity is larger than 1200 mV V‐1dec‐1 at low operating voltage. It can be even further enhanced using an OECT based complementary amplifier, which consists of a p‐type and an n‐type OECT connected in series, as known from digital electronics. The monitoring of cell layer integrity and irreversible disruption of barrier function with the current‐driven OECT is demonstrated for an epithelial Caco‐2 cell layer, showing the enhanced ion‐sensitivity as compared to the standard OECT configuration. As a state‐of‐the‐art application of the current‐driven OECT, the in situ monitoring of reversible tight junction modulation under the effect of drug additives, like poly‐l‐lysine, is discussed. This shows its potential for in vitro and even in vivo toxicological and drug delivery studies

Submicron Vertical Channel Organic Electrochemical Transistors with Ultrahigh Transconductance

Abstract Organic electrochemical transistors (OECTs) belong to the class of electrolyte gated organic transistors (EGOTs) that offer a smooth interface with biology in combination with high transconductance values of typically a few mS. Fabrication‐wise, though, most of the up‐to‐date reported devices are limited to two dimensional structures, where the transistor channel is patterned on the same plane as the source and drain electrodes. Here, a method is introduced for the fabrication of integrated vertical channel OECTs (vOECTs) with submicron channel length. By employing electrodeposition, a vertical channel sandwiched between the source and drain electrodes is created. Channel lengths down to 60 nm are demonstrated, giving rise to ultrahigh transconductance of up to 275 mS. Accounting for the voltage loss on the device connection tracks, an intrinsic transconductance of vOECTs of 500 mS is found. The vOECTs are three‐dimensional transistors finding relevant application in “organ‐on‐a‐chip” and implantable devices, where high amplification and small footprint are demanded

Functional Connectivity of Organic Neuromorphic Devices by Global Voltage Oscillations

Global oscillations in the brain synchronize neural populations and give rise to dynamic binding between different regions. This functional connectivity reconfigures as needed the architecture of the neural network, thereby transcending the limitations of its hardwired structure. Despite the fact that it underlies the versatility of biological computational systems, this concept is not captured in current neuromorphic device architectures. A functional connectivity in an array of organic neuromorphic devices connected through an electrolyte is demonstrated in this work. It is shown that the output of these devices is synchronized by a global oscillatory input despite the fact that individual inputs are stochastic and independent. This temporal coupling is induced at a specific phase of the global oscillation in a way that is reminiscent of phase locking of neurons to brain oscillations. This demonstration provides a pathway toward new neuromorphic architectural paradigms where dynamic binding transcends the limitations of structural connectivity, and could enable architectural concepts of hierarchical information flow

Multiscale real time and high sensitivity ion detection with complementary organic electrochemical transistors amplifier

Though organic electrochemical transistor (OECT)-based ion sensors are attractive for highly sensitive ion detection and monitoring, its limited sensitivity hinders its practical applicability. Here, the authors report real-time, high sensitivity ion detection with complementary OECT amplifiers

Effect of DMSO Solvent Treatments on the Performance of PEDOT:PSS Based Organic Electrochemical Transistors

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

Organic neuromorphic electronics for sensorimotor integration and learning in robotics.

In living organisms, sensory and motor processes are distributed, locally merged, and capable of forming dynamic sensorimotor associations. We introduce a simple and efficient organic neuromorphic circuit for local sensorimotor merging and processing on a robot that is placed in a maze. While the robot is exposed to external environmental stimuli, visuomotor associations are formed on the adaptable neuromorphic circuit. With this on-chip sensorimotor integration, the robot learns to follow a path to the exit of a maze, while being guided by visually indicated paths. The ease of processability of organic neuromorphic electronics and their unconventional form factors, in combination with education-purpose robotics, showcase a promising approach of an affordable, versatile, and readily accessible platform for exploring, designing, and evaluating behavioral intelligence through decentralized sensorimotor integration

Photoinduced Amyloid Fibril Degradation for Controlled Cell Patterning

Amyloid-like fibrils are a special class of self-assembling peptides that have emerged as a promising nanomaterial with rich bioactivity for applications such as cell adhesion and growth. Unlike the extracellular matrix, the intrinsically stable amyloid-like fibrils do not respond nor adapt to stimuli of their natural environment. Here, we designed a self-assembling motif (CKFKFQF), in which a photosensitive o-nitrobenzyl linker (PCL) was inserted. This peptide (CKFK-PCL-FQF) assembled into amyloid-like fibrils comparable to the unsubstituted CKFKFQF and revealed a strong response to UV-light. After UV irradiation, the secondary structure of the fibrils, fibril morphology and bioactivity were lost. Thus, coating surfaces with the pre-formed fibrils and exposing them to UV-light through a photomask generated well-defined areas with patterns of intact and destroyed fibrillar morphology. The unexposed, fibril-coated surface areas retained their ability to support cell adhesion in culture, in contrast to the light-exposed regions, where the cell-supportive fibril morphology was destroyed. Consequently, the photoresponsive peptide nanofibrils provide a facile and efficient way of cell patterning, exemplarily demonstrated for A549 cells. This study introduces photoresponsive amyloid-like fibrils as adaptive functional materials to precisely arrange cells on surface