A Wireless Biosensor Node for In Vivo and Real-Time Plant Monitoring in Precision Agriculture

This article presents a wireless biosensor based on an organic electrochemical transistor, a low-power electronic system, with narrow band (NB)-Internet of Things (IoT)/Cat-M1 radio interface, and server with web interface. The biosensor, implanted in the plant stem, allows the in vivo evaluation of the concentration of nutrients dissolved as cations in the sap. The electronic circuit enables the real-time monitoring of the plant in the crop. The NB-IoT or Cat-M1 link, both available in the system-in-package device selected for the proposed system, ensures almost ubiquitous availability of the network link, without severe limitations on the data payload. The server stores in cloud the data obtained from the field, and a web interface enables the remote monitoring of the plant physiological mechanisms, with consumer devices, such as laptops or smartphones. The low power consumption of the biosensor allows more than three months of battery lifetime, adequate for most seasonal crops. With duty-cycle approach, more than one year of lifetime can be obtained for perennial crops, such as vineyards and orchards. Measurements on KCl solutions showed adequate sensor linearity up to 10-mM K$^+$ concentration, while those performed on a sap of kiwi vines are in agreement with data available in the literature. In vivo measurements carried out on cabbage show how the parameters of the sensor are affected by the circadian cycle. In day time, a reduction of cation concentration, due to water absorption for the photosynthesis and stomatal transpiration, is detected by the wireless-bioristor.