The heart of the device is a tri-layer stack of tungsten diselenide, a semiconductor only a few atoms thick that belongs to the family of transition metal dichalcogenides. Two-dimensional materials like WSe2 are prized in neuromorphic engineering because their entire volume sits at the surface, making their electronic properties exquisitely sensitive to light, electric fields and chemical modification. In their native form, however, WSe2 devices often fall short of the stable, tunable conductance states that artificial synapses demand. The researchers solved this by treating the material with benzyl viologen, a strong electron-donating molecule that donates charge to the WSe2 lattice and shifts its Fermi level, effectively engineering the carrier polarity of the channel and setting the stage for the dramatic optical behaviors that follow.

Before any synaptic claims could be made, the team had to prove the material survived the doping process intact. Atomic force microscopy confirmed the structural integrity and surface morphology of the tri-layer films, while Raman spectroscopy verified that the crystal lattice remained high quality after exposure to the benzyl viologen treatment. On the electrical side, gate-dependent transfer curves and current-voltage measurements mapped out how the doping transformed the device’s behavior, and the researchers constructed an energy band diagram showing the Fermi level shift that the molecular dopants induce. This combination of structural and electrical characterization matters because any degradation of the delicate 2D lattice would undermine the reproducibility that real neuromorphic circuits require.

The most striking results emerge when light hits the device. The BV-doped WSe2 synapse responds strongly to both visible and deep-ultraviolet illumination, but it is the deep-ultraviolet response that gives the device its memory. Under DUV light, charges become trapped within the material system, and these trapped charges persist long after the light is switched off, producing a stable conductance state that functions as a nonvolatile memory. In other words, a flash of ultraviolet light writes information into the device, and the device holds that information without power, much as a biological synapse retains the trace of a past experience. This optically programmable memory is what allows the same physical structure to act simultaneously as a photodetector and a synaptic element.

When stimulated with sequences of optical pulses rather than continuous illumination, the device reproduces hallmark behaviors of biological synapses. Paired-pulse facilitation, a form of short-term plasticity in which the second of two closely spaced signals produces a larger response than the first, appears naturally in the device’s conductance dynamics. With longer or more intense stimulation, the device exhibits long-term potentiation and long-term depression, the persistent strengthening and weakening of connection strength that neuroscientists consider the cellular basis of learning and memory. Crucially, the magnitude of the response is tunable: by controlling the duration of the deep-ultraviolet pulses, the researchers increased the device’s photoresponse from 25.2 percent to 1438.7 percent, a dynamic range wide enough to encode many distinct synaptic weights.

That tunability translates directly into computational capability. The team demonstrated that the device can perform a logic OR gate operation, outputting a high signal when either of two inputs is present, and that it can carry out selective alphabet recognition, distinguishing among written characters based on the optical signatures stored in its conductance states. These demonstrations show that the device is not merely a passive memory element but an active processing unit, capable of the kind of in-memory logic that could dramatically reduce the energy overhead of edge-computing systems, where data must be processed locally under strict power budgets rather than shipped to energy-hungry data centers.

To test whether the device’s synaptic behavior could scale to meaningful machine learning, the researchers implemented its experimentally measured synaptic weight characteristics in an artificial neural network and trained that network to identify handwritten digits from the MNIST dataset, a standard benchmark in computer vision. The simulated network achieved an accuracy of 92 percent, and the team validated the learning process through epoch-dependent learning curves and confusion matrix analysis, confirming that the network’s errors were distributed in the way one expects from a genuinely learning system rather than a lucky configuration. The result is significant because it grounds the device physics in a concrete application: the same conductance modulation that the researchers measured in the laboratory can, in principle, serve as the adjustable weights that artificial neural networks rely on.

The broader significance of the work lies in its multifunctionality. Most neuromorphic devices reported to date specialize in one role, whether as memristors, phase-change memories or electrochemical transistors, and require separate photonic or electronic circuitry to interface with the outside world. By combining optical sensing, nonvolatile charge-trapping memory, short- and long-term plasticity, logic operation and pattern recognition in a single doped 2D material platform, the WSe2 synapse points toward integrated intelligent sensors that could see, remember and compute in one package. Such devices would be natural fits for autonomous drones, biomedical implants and environmental monitors, where every milliwatt saved extends operational life.

There are, of course, hurdles between a laboratory demonstration and deployable technology. The device relies on exquisitely controlled chemical doping of atomically thin crystals, and scaling such processes to wafer-scale manufacturing while maintaining the uniformity that large neural networks demand remains an open challenge in the 2D materials community. The 92 percent MNIST accuracy, while respectable, still trails the best software-based networks, suggesting that device variability and nonlinearity in the conductance updates will need further engineering. The published version of the paper is also an early-release, peer-reviewed accepted manuscript that may undergo further edits before the final version of record appears, so specific figures could be refined.

Even so, the study adds an important entry to the growing catalog of optoelectronic synapses, and its use of benzyl viologen doping to engineer carrier polarity in tri-layer WSe2 gives other researchers a concrete chemical lever to pull. The work was supported by the Korea Basic Science Institute through a National Research Facilities and Equipment Center grant funded by the Korean Ministry of Education, by an IITP Information Technology Research Center grant from the Ministry of Science and ICT, and by the ongoing research funding program of King Saud University in Riyadh. As artificial intelligence migrates from the cloud toward the edge, devices that can be programmed by nothing more than pulses of light, and that learn the way neurons do, may prove to be exactly the kind of hardware the next generation of intelligent machines is waiting for.

Subject of Research: Optoelectronic synaptic devices based on doped two-dimensional tungsten diselenide for neuromorphic computing and logic operations

Article Title: A multifunctional optoelectronic synaptic device for logic operation and neuromorphic computing

Article References: Dastgeer, G., Nisar, S., Fatima, I., Ali, R. F., Rabani, I., Hussain, K., Alsalme, A., & Eom, J. (2026). A multifunctional optoelectronic synaptic device for logic operation and neuromorphic computing. Advanced Composites and Hybrid Materials. https://doi.org/10.1007/s42114-026-02103-z

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02103-z

Keywords: neuromorphic computing, optoelectronic synapse, tungsten diselenide, WSe2, benzyl viologen doping, two-dimensional materials, memristor, synaptic plasticity, charge trapping, artificial neural network, MNIST, logic gates

Polyaniline belongs to a family of materials called conducting polymers, which behave in many respects like reactive macromolecular gels when wet. When an electric current is passed through them, their polymer chains undergo oxidation or reduction, gaining or losing electrons. This triggers the exchange of counterions and solvent molecules with the surrounding electrolyte, causing the chains to swell, shrink, relax or compact. The researchers draw a striking parallel with living cells: in both cases, electrical stimuli drive chemical reactions in macromolecular chains that produce conformational movement, ionic exchange and solvent exchange, in other words, a reversible change in the chemical composition of the entire polymer-ion-solvent system. It is precisely this biomimetic quality that makes polyaniline attractive for applications ranging from sensors and artificial muscles to supercapacitors, smart windows and drug delivery systems.

The chemical mechanism underlying the switching is formally described as an anion-driven process. In the reduced state, polyaniline chains carry sigma bonds between consecutive monomeric units, allowing free rotation and numerous conformations. Upon oxidation, radical cations form along the chain, introducing new pi bonds that restrict rotation and effectively turn the chain into a molecular motor. To maintain charge neutrality, chloride anions from the 1 M hydrochloric acid electrolyte diffuse into the polymer, and water molecules follow for osmotic balance. During reduction, the reverse occurs: protons are incorporated, and chloride ions and water are expelled. The multistep redox chemistry connects three canonical forms of the polymer, leucoemeraldine, emeraldine and pernigraniline, with anodic peaks observed at 0.30 V and 0.53 V and corresponding reduction peaks at 0.44 V and 0.078 V in the team’s cyclic voltammograms.

The central innovation of the study lies in coulovoltammetry, a technique in which the cyclic voltammogram is integrated to plot the consumed charge directly against the applied potential. The resulting closed or open loops encode an enormous amount of information. A perfectly closed loop indicates that the anodic and cathodic charges are equal, meaning only reversible redox processes are occurring. Between 0 and -0.3 V on the cathodic side, and up to 0.7 V on the anodic side, the team found just such a window of pure reversibility for polyaniline in hydrochloric acid. Beyond these limits, new irreversible processes appear, identified as hydrogen evolution on the cathodic side and overoxidation or oxygen evolution on the anodic side, whose associated charges grow exponentially with increasingly extreme potential limits.

More remarkably still, the coulovoltammogram allows the authors to separate four distinct structural faradaic processes, in line with the Electrochemically Stimulated Conformational Relaxation model developed by Toribio Otero and colleagues. Starting from the fully oxidized state, the fast reduction-shrinking stage proceeds under diffusion control of counterions leaving the swelling film. Once the shrinking chains close the gel structure at a characteristic closing potential, further reduction cannot stop but slows dramatically, because the departing anions must physically push polymer chains apart to open their exit pathways. This slow reduction-compaction stage even persists into the beginning of the subsequent anodic sweep, a phenomenon the team calls reduction electrochemical inertia, which they confirmed using chronocoulograms showing continuous faradaic charge decay. Conversely, oxidation begins with a slow relaxation process that opens the compact structure and generates free volume for incoming anions, followed by fast oxidation-swelling, and finally an oxidation inertia that continues past the anodic potential limit into the cathodic sweep.

The analysis also yielded an unexpected energetic finding. By integrating the coulovoltammetric areas, the researchers calculated the electrical energy consumed during oxidation and reduction across different potential windows. The reduction energies turned out to be almost twice the oxidation energies, revealing a pronounced charge symmetry but energy asymmetry in the reaction. The authors attribute this asymmetry to the inherently different structural processes on the two sides of the cycle, including conformational relaxation, swelling, shrinking, compaction, ion trapping and electrochemical inertia, compounded by osmotic solvent exchange. Intriguingly, they suggest this mirrors the asymmetry of reaction-driven biological functions, noting that muscles perform work during contraction but not relaxation, and that ionic channels in living systems pass ions preferentially in one direction.

Perhaps the most consequential demonstration is that polyaniline’s electrochemical reaction is self-sensing, meaning it can report on its own working conditions without any additional sensor hardware. The team derived theoretical sensing equations from the reaction kinetics and Faraday’s laws, then verified them experimentally. The charge consumed by the reversible reaction showed a clean double-logarithmic linear dependence on the scan rate, with an excellent correlation coefficient of 0.993, and the same held true when frequency was used as the electrical variable. At slower scan rates, the reaction has more time to drive deep conformational changes, exchange large numbers of ions and solvent molecules, and consume correspondingly more charge and energy; at faster rates, the polymer only partially switches. The consumed electrical energy likewise varied linearly in semi-logarithmic plots against scan rate, with distinct sensitivity slopes of -6.77 J g-1 per logarithmic unit for reduction and -2.15 for oxidation.

The same logic extended to chemical and thermal conditions. When the electrolyte concentration was varied from 1 M down to 0.075 M hydrochloric acid, the consumed charge increased in a double-logarithmic fashion with concentration, because higher concentrations provide more chemical energy for deeper oxidation and greater counterion uptake. The consumed energy per gram of polymer also rose linearly with concentration, with sensitivity slopes of 2.948 J g-1 per logarithmic unit for reduction and 0.608 for oxidation. Temperature produced analogous behaviour: as the working temperature increased, thermal energy pushed the reaction toward deeper redox states, and the charge obeyed the semilogarithmic Arrhenius-derived sensing equation, with a temperature sensitivity slope of -601.28, while consumed energy rose linearly by 0.152 J g-1 per degree Celsius for reduction and 0.061 for oxidation.

Because the sensing parameters here are simply the consumed charge and the consumed electrical energy during the reaction, any electrochemical device built on polyaniline, whether a supercapacitor electrode, an actuator, an electrochromic window or a drug delivery platform, could in principle monitor its own instantaneous operating state without separate instrumentation. The authors emphasize that this differs fundamentally from conventional chemical sensing, which aims to identify or quantify specific analytes; the goal instead is a material whose reaction is intrinsically aware of the energetic and chemical ambient in which it operates, much as biological macromolecular motors simultaneously generate actuation and sense their surroundings through the same underlying reaction.

The study represents the first systematic coulovoltammetric analysis of chemically synthesized polyaniline, extending to this polymer a methodology previously applied mainly to polypyrrole, and tackling the added complexity of polyaniline’s multistep proton-coupled redox transitions. The researchers synthesized the material by chemical oxidative polymerization of aniline with ammonium persulphate in hydrochloric acid, characterized it by FTIR spectroscopy, dielectric spectroscopy, thermogravimetric analysis and electron microscopy, and coated it onto glassy carbon electrodes for electrochemical testing with a Zennium Pro workstation. Supported by fellowships from the University Grants Commission and the Kerala State Council for Science, Technology and Environment, the work contributes both to the fundamental structural electrochemistry of conducting polymers and, the authors argue, to the development of soft, wet, reactive multifunctional biomimetic devices that could reshape soft robotics, bioelectronics and biomedicine in the years ahead.

Subject of Research: Coulovoltammetric analysis of structural electrochemistry, charge-energy asymmetry and reactive self-sensing capabilities of polyaniline

Article Title: Understanding the electrochemistry of polyaniline structural processes, charge, energy and reactive sensing capabilities through coulovoltammetry

Article References: Sidheekha, M. P., Rajan, L., Prakash, S., Shabeeba, A., & Ismail, Y. A. (2026). Understanding the electrochemistry of polyaniline structural processes, charge, energy and reactive sensing capabilities through coulovoltammetry. Discover Electrochemistry, 3(1), Article 84. https://doi.org/10.1007/s44373-026-00172-9

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00172-9

Keywords: polyaniline, coulovoltammetry, conducting polymers, structural electrochemistry, redox switching, ESCR model, energy asymmetry, self-sensing materials, biomimetic devices, electrochemical sensors, charge trapping, conformational relaxation