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Abstract Printable and wearable plant sensors offer an approach for collecting critical environmental data at high spatial resolution to understand plant conditions and aid land management practices. Here, screen printed capacitive devices that can measure relative humidity (RH) directly at the plant‐environment interface, are demonstrated in an ultra‐thin (<6 µm) form factor. Using screen printing and a temporary tattoo transfer process, a simple technique is established to: 1) enclose printed electronic features between two layers of ethyl cellulose (EtC), 2) mount printed microparticle carbon‐based electronics onto a variety of plant structures, and 3) dramatically increase the capacitance and sensitivity for humidity sensors when compared to unencapsulated devices. This sandwich tattoo capacitor (STC) platform exhibits an RH sensitivity up to 1000 pF/%RH and stability while mounted to living plant leaves over several days. Electrochemical impedance spectroscopy (EIS) validates the formation of electric double layers within the EtC films that encapsulate the printed electrodes providing tunable capacitance values based on the ionic concentration of the device transfer fluid. 

Abstract A key challenge in bioelectronics is to establish and improve the interface between electronic devices and living tissues, enabling a direct assessment of biological systems. Sensors integrated with plant tissue can provide valuable information about the plant itself as well as the surrounding environment, including air and soil quality. An obstacle in developing interfaces to plant tissue is mitigating the formation of fibrotic tissues, which can hinder continuous and accurate sensor operation over extended timeframes. Electronic systems that utilize suitable biocompatible materials alongside appropriate fabrication techniques to establish plant-electronic interfaces could provide for enhanced environmental understanding and ecosystem management capabilities. To meet these demands, this study introduces an approach for integrating printed electronic materials with biocompatible cryogels, resulting in stable implantable hydrogel-based bioelectronic devices capable of long-term operation within plant tissue. These inkjet-printed cryogels can be customized to provide various electronic functionalities, including electrodes and organic electrochemical transistors (OECTs), that exhibit high electrical conductivity for embedded conducting polymer traces (up to 350 S/cm), transconductance for OECTs in the mS range, a capacitance of up to 4.2 mF g⁻¹in suitable structures, high stretchability (up to 330% strain), and self-healing properties. The biocompatible functionalized cryogel-based electrodes and transistors were successfully implanted in plant tissue, and ionic activity in tomato plant stems was collected for over two months with minimal scar tissue formation, making these cryogel-based printed electronic devices excellent candidates for continuous, in-situ monitoring of plant and environmental status and health. 

Abstract Low‐cost biosensors that can rapidly and widely monitor plant nutritional levels will be critical for better understanding plant health and improving precision agriculture decision making. In this work, fully printed ion‐selective organic electrochemical transistors (OECTs) that can detect macronutrient concentrations in whole plant sap are described. Potassium, the most concentrated cation in the majority of plants, is selected as the target analyte as it plays a critical role in plant growth and development. The ion sensors demonstrate high current (170 µA dec⁻¹) and voltage (99 mV dec⁻¹) sensitivity, and a low limit of detection (10 × 10⁻⁶ m). These OECT biosensors can be used to determine potassium concentration in raw sap and sap‐like aqueous environments demonstrating a log‐linear response within the expected physiological range of cations in plants. The performance of these printed devices enables their use in high‐throughput plant health monitoring in agricultural and ecological applications. 

Abstract Implantable electrophoretic drug delivery devices have shown promise for applications ranging from treating pathologies such as epilepsy and cancer to regulating plant physiology. Upon applying a voltage, the devices electrophoretically transport charged drug molecules across an ion‐conducting membrane out to the local implanted area. This solvent‐flow‐free “dry” delivery enables controlled drug release with minimal pressure increase at the outlet. However, a major challenge these devices face is limiting drug leakage in their idle state. Here, a method of reducing passive drug leakage through the choice of the drug co‐ion is presented. By switching acetylcholine's associated co‐ion from chloride to carboxylate co‐ions as well as sulfopropyl acrylate‐based polyanions, steady‐state drug leakage rate is reduced up to sevenfold with minimal effect on the active drug delivery rate. Numerical simulations further illustrate the potential of this method and offer guidance for new material systems to suppress passive drug leakage in electrophoretic drug delivery devices.