In-memory and neuromorphic computing based on organic synaptic transistors promise to overcome the speed, energy, and bandwidth limitations of von Neumann architectures, yet electrically driven devices remain constrained by the same bottlenecks affecting purely electronic transistors. Photonic synaptic devices, using light as both input and output carrier, offer signal transmission, which is anti-interference, long-distance, low-loss, massively parallel and with no need for impedance-matching between computing units, positioning photonic neuromorphic hardware as a natural evolution of information technology. Building on Organic Photonic Synaptic Transistors (OPSTs), which combine electrical and optical stimulation with an electrical readout, this perspective introduces the Photo-Synaptic Organic Light-Emitting Transistor (PS-OLET), that merges optical sensing, in-device information processing, synaptic plasticity, and light emission within a single, scalable, planar transistor architecture. We review the material and device strategies used to achieve optical triggering in OPSTs and describe how the intrinsic light-generation capability of Organic Light-Emitting Transistors can be merged with these synaptic mechanisms to realize a genuinely dual-output optoelectronic device relevant for intelligent-display applications. We further propose PS-OLETs as physical nodes for photonic Reservoir Computing: by integrating electrical and optical input, nonlinear processing, and electrical and optical output within one device, PS-OLETs can act as low-loss, low-latency optoelectronic reservoir units, overcoming the need for external light sources and the spatial constraints of memristor- or waveguide-based architectures. Within the appropriate signal bandwidth, the PS-OLET-based reservoir can operate with intrinsic timescales matched to the input temporal features, enabling optimal memory capacity. We also discuss how PS-OLET networks could support fully analogic, reconfigurable reservoir computing systems combining high state richness and massively parallel, distributed processing. Extending the spectral response to the visible and near-infrared range, exploiting circularly polarized light for chiro-optical synaptic functions, and integrating additional sensing modalities are expected to establish PS-OLETs as a foundational technology for next-generation photonic neuromorphic hardware.
Abstract Managing optimal moisture balance is essential for chronic wound healing, yet current clinical assessments are often subjective and intermittent. This study reports the development of a high-performance, flexible resistive moisture sensor designed for real-time, quantitative wound monitoring. The active sensing layer consists of a lithium-ion (Li + ) functionalized Mo 2 CT X MXene and polyaniline (PANI) composite. Li + intercalation was utilized to expand the MXene interlayer spacing, enhancing water adsorption and ion transport. Simultaneously, in situ polymerized PANI was introduced to provide stable proton-conductive pathways. Current–voltage characterization verified that the Li + –Mo 2 CT X /PANI composite forms robust Ohmic contacts with the electrodes, exhibiting over a 40-fold enhancement in baseline electrical conductance compared to pristine Mo 2 CT X . The composite was integrated onto screen-printed circular interdigitated electrodes on a flexible PET substrate and encapsulated with poly(diallyldimethylammonium chloride) (PDAC). This protective PDAC layer acts as a semi-permeable moisture-diffusion barrier that regulates water molecule transport, prevents surface fouling and uncontrolled hydration saturation, and ensures environmental stability without compromising response speed. The sensor demonstrates a linear response across a wide relative humidity (RH) range of 20%–80%, featuring sensitivity of approximately 2.0 Δ R /%ΔRH, with a rapid response time of ∼1 s and a recovery time of ∼11 s. The device demonstrates high mechanical flexibility, and stable operation over a 15 d period. Real-time assessments using finger-touch tests and PVA-hydrogel wound models successfully distinguished between dry, normal, and wet clinical states. The superior performance is attributed to the synergistic effects of Li + -assisted interlayer hydration, Grotthuss-type proton hopping, and moisture-induced PANI protonation. These findings position the Li + –Mo 2 CT X /PANI composite as a promising candidate for next-generation smart dressings in digital wound management.
Abstract Graphene-based inks have emerged as promising functional materials for printed and flexible electronics because of their electrical, mechanical, and chemical properties, together with their compatibility with solution-based processing. Among the various graphene-based materials, graphene oxide (GO), reduced graphene oxide (rGO), graphene flakes, and graphene-based composites are particularly attractive for ink formulations due to their tunable dispersibility, electrical conductivity, and processability. This review discusses graphene-based inks from the perspective of material selection, ink formulation, and printability, with a focus on flexible sensor applications. First, the key graphene derivatives used in printable inks are outlined, followed by a discussion of their electrical, optical, thermal, and mechanical properties in the context of printed films. The major synthesis routes, including top-down and bottom-up approaches, are then compared with an emphasis on scalability and compatibility with ink-based processing. Particular attention is given to ink formulation strategies, including solvent selection, binder and additive incorporation, rheological control, dispersion stability, and post-print processing such as thermal annealing, chemical reduction, and photonic treatment. The role of these factors in determining print quality, interflake charge transport, and device performance is highlighted. Representative applications in flexible sensing, including biosensors, gas, humidity, strain, and pressure sensors, are also reviewed. Finally, current challenges related to dispersion stability, conductivity–printability trade-offs, reproducibility, and long-term device reliability are discussed, together with future directions involving hybrid inks, predictive rheological modelling, and sustainable processing routes. Overall, graphene-based inks offer a versatile platform for the development of printed and wearable sensors, with further advances in formulation, processing, and scale-up needed for broader technological adoption.
Abstract Amorphous indium gallium zinc oxide (IGZO) based flexible and robust chemiresistive NO 2 gas sensors prepared on a polyimide substrate are presented in this work. A different target composition of IGZO (In:Ga:Zn ratio of 1:1:5) than the usually reported In:Ga:Zn:1:1:1 composition for gas sensing is explored in the present study. IGZO (115) composition has been reported for transparent thin film devices and circuits previously. In fact, this is the first study to explore this particular composition for the fabrication of flexible gas sensors. The devices are semi-transparent, adding another functionality that can be useful for see-through devices. Therefore, this study can open new paths for transparent, flexible, and fully integrated all IGZO based devices and circuits. The sensor gives an excellent response to sub-ppm exposures of NO 2 gas. A 262% increase in the resistance of the device is observed for 1 ppm NO 2 exposure at 125 °C which is amongst the best responses reported for metal oxide based flexible NO 2 gas sensors. The sensor device shows a highly linear response ( R 2 = 0.9928) to sub-ppm NO 2 concentrations with an experimentally observable limit of detection reaching 100 ppb. Furthermore, the devices are robust in the sense that they can be subjected to a large number of bending cycles and multiple squeegee cycles and can still retain good responsivity. Squeegeeing is one of the most commonly used methods for sticking tapes and stickers on flat surfaces. This is the first report where a gas sensor has been subjected to squeegee cycles to demonstrate its capabilities to withstand extreme mechanical forces. The proposed devices have potential to be used as sticker type gas sensing devices as their capability to withstand bending can allow rolling of sensor arrays for storage and transportation while their capability to withstand squeegeeing can be useful during sticking the devices.
