Transistor‐based ion sensors have evolved significantly, but the best‐performing ones rely on a liquid electrolyte as an internal ion reservoir between the ion‐selective membrane and the channel. This liquid reservoir makes sensor miniaturization difficult and leads to devices that are bulky and have limited mechanical flexibility, which is holding back the development of high‐performance wearable/implantable ion sensors. This work demonstrates microfabricated ion‐selective organic electrochemical transistors (OECTs) with a transconductance of 4 mS, in which a thin polyelectrolyte film with mobile sodium ions replaces the liquid reservoir. These devices are capable of selective detection of various ions with a fast response time (≈1 s), a super‐Nernstian sensitivity (85 mV dec⁻¹), and a high current sensitivity (224 µA dec⁻¹), comparing favorably to other ion sensors based on traditional and emerging materials. Furthermore, the ion‐selective OECTs are stable with highly reproducible sensitivity even after 5 months. These characteristics pave the way for new applications in implantable and wearable electronics.

Electrode arrays that interface with peripheral nerves are used in the diagnosis and treatment of neurological disorders; however, they require complex placement surgeries that carry a high risk of nerve injury. Here we leverage recent advances in soft robotic actuators and flexible electronics to develop highly conformable nerve cuffs that combine electrochemically driven conducting-polymer-based soft actuators with low-impedance microelectrodes. Driven with applied voltages as small as a few hundreds of millivolts, these cuffs allow active grasping or wrapping around delicate nerves. We validate this technology using in vivo rat models, showing that the cuffs form and maintain a self-closing and reliable bioelectronic interface with the sciatic nerve of rats without the use of surgical sutures or glues. This seamless integration of soft electrochemical actuators with neurotechnology offers a path towards minimally invasive intraoperative monitoring of nerve activity and high-quality bioelectronic interfaces.

Organic electrochemical transistors (OECTs) are a burgeoning biosensing transducer platform due to their intrinsic amplification, high transconductance, and biocompatibility. To be successful in real world biosensing applications, however, stable performance should be demonstrated to avoid false analyte readings that could lead to dangerous misdiagnosis. This work demonstrates the stability of carefully prepared OECTs using commercially available PEDOT:PSS as the channel layer. These devices exhibit more than 99% retention of the baseline current over 50 transfer curve cycles and, importantly, after several changes in electrolyte solution. Furthermore, impressive stability is demonstrated during continuous measurements of the drain current. These results show that PEDOT:PSS OECTs are ready for biosensing applications requiring accurate continuous monitoring.

By simultaneously transducing and amplifying, transistors offer advantages over simpler, electrode-based transducers in electrochemical biosensors. However, transistor-based biosensors typically use static (i.e., DC) operation modes that are poorly suited for sensor architectures relying on the modulation of charge transfer kinetics to signal analyte binding. Thus motivated, here, we translate the AC “pulsed potential” approach typically used with electrochemical aptamer-based (EAB) sensors to an organic electrochemical transistor (OECT). Specifically, by applying a linearly sweeping square-wave potential to an aptamer-functionalized gate electrode, we produce current modulation across the transistor channel two orders of magnitude larger than seen for the equivalent, electrode-based biosensor. Unlike traditional EAB sensors, our aptamer-based OECT (AB-OECT) sensors critically maintain output current even with miniaturization. The pulsed transistor operation demonstrated here could be applied generally to sensors relying on kinetics-based signaling, expanding opportunities for noninvasive and high spatial resolution biosensing.

A quantitative and analytical investigation on the conduction mechanism in p-type cuprous oxide (Cu₂O) thin films is performed based on analysis of the relative dominance of trap-limited and grain-boundary-limited conduction. It is found that carrier transport in as-deposited Cu₂O is governed by grain-boundary-limited conduction (GLC), while after high-temperature annealing, GLC becomes insignificant and trap-limited conduction (TLC) dominates. This suggests that the very low Hall mobility of as-deposited Cu₂O is due to significant GLC, and the Hall mobility enhancement by high-temperature annealing is determined by TLC. Evaluation of the grain size and the energy barrier height at the grain boundary shows an increase in the grain size and a considerable decrease in the energy barrier height after high-temperature annealing, which is considered to be the cause of the significant reduction in the GLC effect. Additionally, the density of copper vacancies was extracted; this quantitatively shows that an increase in annealing temperature leads to a reduction in copper vacancies.

Wearable sensors have evolved significantly, making personalized medicine and real-time disease management possible. However, current digital healthcare is limited to only certain diseases, such as diabetes, due to the lack of mature technologies that can detect small biomolecules. In particular, despite the early detection of chronic kidney disease (CKD) being significant in preventing life-threatening end-stage kidney disease, the development of wearable sensors for CKD monitoring is still in the early stages. In this Perspective, we propose a wearable digital healthcare concept for non-invasive, continuous CKD monitoring, discuss optimal biofluids, biomarkers and bioreceptors to create a wearable CKD sensing platform, and provide insight into potential challenges faced by the technology as well as opportunities.