Plant growth and development are negatively affected by a wide range of external stresses, including water deficits. Especially, plants generally reduce the stomatal aperture to decrease transpiration levels upon drought stress. Advanced technologies, such as wireless communications, the Internet of things (IoT), and smart sensors have been applied to practical smart farming and indoor planting systems to monitor plants' signals effectively. In this study, we develop a flexible polyimide (PI)-based sensor for real-time monitoring of water conditions in tobacco plants. The stoma response, by which a plant adjusts to drought stress to maintain homeostasis, can be confirmed through the examination of evaporated water. Using a flexible PI-based sensor, a plant's response variation is translated into an electrical signal. The sensors are integrated with a Bluetooth (BLE) module and a processing module and show potential as smart real-time water sensors in smart farms.

Molybdenum disulfide (MoS) field-effect transistor (FET)-based biosensors have attracted significant attention as promising candidates for highly sensitive, label-free biomolecule detection devices. In this paper, toward practical applications of biosensors, we demonstrate reliable and quantitative detection of a prostate cancer biomarker using the MoS FET biosensor in a nonaqueous environment by reducing nonspecific molecular binding events and realizing uniform chemisorption of anti-PSA onto the MoS surface. A systematic and statistical study on the capability of the proposed device is presented, and the biological binding events are directly confirmed and characterized through intensive structural and electrical analysis. Our proposed biosensor can reliably detect various PSA concentrations with a limit of 100 fg/mL. Moreover, rigorous theoretical simulations provide a comprehensive understanding of the operating mechanism of the MoS FET biosensors, and further suggests the enhancement of the sensitivity through engineering device design parameters.

Wearable on‐skin electronic devices that can monitor temperature in real time are of significant interest for personalized mobile health monitoring. Here, a flexible temperature sensor directly patterned by laser‐induced carbonization on Kapton polyimide films integrated with flexible printed circuit boards is reported. The proposed sensor design possessing high resistance values exhibits high‐linear and stable response to temperatures when integrated with flexible printed circuit boards (FPCBs) to enable continuous monitoring. The anisotropic conductive film bonding technique is used to obtain the stable real‐time monitoring data under various complex environments. The sensor integration with a wearable patch based FPCB establishes conformal contacts with human skin and allows wireless sensing capabilities smoothly in real time. This kind of approach can enable multifunctional sensors to be directly laser patterned on FPCBs without any additional interfacing.

Real-time temperature monitoring of individual blood packages capable of wireless data transmission to ensure the safety of blood samples and minimize wastes has become a critical issue in recent years. In this work, we propose flexible temperature sensors using silver nanowires (NWs) and a flexible colorless polyimide (CPI) film integrated with a wireless data transmission circuit. The unique design of the temperature sensors was achieved by patterning Ag NWs using a three-dimensional printed mold and embedding the patterned Ag NWs in the CPI film (p-Ag NWs/CPI), which resulted in a flexible temperature sensor with electrical, mechanical, and temperature stability for applications in blood temperature monitoring. Indeed, a reliable resistance change of the p-Ag NWs/CPI was observed in the temperature range of −20 to 20 °C with a robust bending stability of up to 5000 cycles at 5 mm bending radius. Real-time and wireless temperature monitoring using the p-Ag NWs/CPI was demonstrated with the packages of rat blood. The result revealed that the stable and consistent temperature monitoring of individual blood packages could be achieved in a blood box, which was mainly attributed to the conformal attachment of the p-Ag NWs/CPI to different packages in a blood container.

With an increasing demand for artificial intelligence, the emulation of the human brain in neuromorphic computing has led to an extraordinary result in not only simulating synaptic dynamics but also reducing complex circuitry systems and algorithms. In this work, an artificial electronic synaptic device based on a synthesized MoS2 memristor array (4 × 4) is demonstrated; the device can emulate synaptic behavior with the simulation of deep neural network (DNN) learning. MoS2 film is directly synthesized onto a patterned bottom electrode (Pt) with high crystallinity using sputtering and CVD. The proposed MoS2 memristor exhibits excellent memory operations in terms of endurance (up to 500 sweep cycles) and retention (~ 104) with a highly uniform memory performance of crossbar array (4 × 4) up to 16 memristors on a scalable level. Next, the proposed MoS2 memristor is utilized as a synaptic device that demonstrates close linear and clear synaptic functions in terms of potentiation and depression. When providing consecutive multilevel pulses with a defined time width, long-term and short-term memory dynamics are obtained. In addition, an emulation of the artificial neural network of the presented synaptic device showed 98.55% recognition accuracy, which is 1% less than that of software-based neural network emulations. Thus, this work provides an enormous step toward a neural network with a high recognition accuracy rate.

Epidermal and wearable electronic sensor technologies have gained extensive interest in recent years owing to deliver real-time healthcare information to the personalized smartphone. Herein, we proposed a fully integrated wearable smart patch-based sensor system with Kirigami-inspired strain-free deformable structures having temperature and humidity sensors along with a commercial acceleration sensor. The presented fully integrated wearable sensor system easily attaches to the skin to accurately determine the body information, and integrated circuit including read-out circuit and wireless communication transfer medical information (temperature, humidity, and motion) to mobile phone to assist with emergencies due to "unpredictable" deviations and to aid in medical checkups for vulnerable patients. This article addresses the challenge of all-day continuous monitoring of human body biological signals by introducing the well-equipped breathable (water permeability ∼ 80 gm −1 •h −1), excellent adhesion to the skin (peel strength < 200 gf/12 mm), biocompatible, and conformable smart patch that can absorb the moisture (sweat) generated from the skin without any harshness and allowing the users' to continuously monitor the early detection of diagnosis. Furthermore, the proposed patchbased medical device enables wireless sensing capabilities in response to rapid variation, equipped with a customized circuit design, low-power Bluetooth module, and a signal processing integrated circuit mounted on a flexible printed circuit board. Thus, a unique platform is established for multifunctional sensors to interface with hard electronics, providing emerging opportunities in the biomedical field as well as Internet-of-Things applications.

Wearable devices are widely used in the smart healthcare monitoring system to detect changes in user parameters through applications such as wristwatches, bands, and clothing electronic skin. In addition, multimode devices enable monitoring of vital signs, helping diagnose and prevent diseases. A wearable device detects the user's biological signals such as body temperature, movement, heartbeat, and humidity level, transmits the information to the mobile phone, and sends the information to an emergency center/family/clinician through cloud computing or wireless communication systems. This all‐day monitoring system enables the user's status information to be monitored 24 h a day to ensure appropriate treatment, thereby facilitating highly personalized care due to its human‐centricity. When integrated with higher‐level infrastructure, it is expected to be useful in healthcare scenarios, providing benefits to multiple stakeholders. In addition, it will help protect people exposed to potentially life‐threatening environments such as military personnel, first responders, and deep‐sea and space explorers. In this review, the components for implementing an all‐day monitoring system are described, including the electrode design strategy for realizing a skin attachable e‐skin device. Issues related to flexible storage devices and recent research results are also discussed.

Molybdenum disulfide (MoS2) semiconductors have closely been studied for potential applications in detectors, optoelectronics, and flexible electronics due to its high electrical and robust mechanical performance. Herein, the first experimental study of the high‐speed ultrasound wave detection by the combinational structure of flexible MoS2 field‐effect transistor (FET) and piezoelectric device based on polyvinylidene fluoride trifluoro ethylene P(VDF‐TrFE) is reported. The proposed flexible MoS2 based FET device exhibits maximum mobility of 18.12 cm2 Vs−1, high on/off current ratio of ≈105, high robustness over mechanical tests, and excellent gate‐pulsed switching behavior at different frequencies (10, 100, and 500 kHz), thus, utilized as supporting electronics to detect ultrasound wave at high‐speed. The ultrasound waves are applied to the self‐assembled piezoelectric device under different power scales (0 ≈ 1.5 W cm−2) and the transfer curve of the proposed FET is analyzed. The results show a clear detection of ultrasound waves with high stability and excellent linearity in terms of threshold voltage (Vth) shift and drain current (Ids) under different power levels. Also, the pulsed gate‐switching behavior is analyzed and the ultrasound detection with high stability is observed at high‐speed switching, thus, enabling the development of applications in high‐speed electronic devices and biomedical imaging tools.