Title : 4.0 wearable plant sensor: solving obstacles toward the long-term, accurate, and remote monitoring of water loss from plants under variable microclimate
Abstract:
Impedimetric wearable sensors are a promising strategy for determining the loss of water content (LWC) from leaves because they can afford on-site and nondestructive quantification of cellular water from a single measurement. Because the water content is a key marker of leaf health, monitoring of the LWC can lend key insights into daily practice in precision agriculture, toxicity studies, and the development of agricultural inputs. Ongoing challenges with this monitoring are the on-leaf adhesion, compatibility, scalability, and reproducibility of the electrodes, especially when subjected to long-term measurements. This work introduces a set of sensing material, technological, and data processing solutions that overwhelm such obstacles. Mass-production-suitable electrodes consisting of stand-alone Ni films obtained by well-established microfabrication methods enabled reproducible determination of the LWC from soy leaves with optimized sensibilities of 27.0 kΩ %–1. The electrodes operated through direct transfer of the conductive materials on hairy soy leaves using ordinary adhesive tape. The freestanding design of the electrodes was further key to delivering high on-leaf adhesion and long-term compatibility. Their impedances remained unchanged under the action of wind at velocities of up to 2.00 m s–1, whereas X-ray nanoprobe fluorescence assays allowed us to confirm the sensor design compatibility from the monitoring of the soy leaf health in an electrode-exposed area. We used a handheld and low-power potentiostat with a wireless connection to a smartphone to determine the LWC over 24 h. Impressively, a machine-learning model was able to convert the sensing and reproducible responses in controlled conditions (30 and 20 °C) into a simple mathematical 3D equation that gauged the impairments on the water content with reduced root-mean-square errors (0.1% up to 0.3%). Next, analyses under variable climatic conditions were performed to scrutinize the applicability of the sensor. The Ni films were covered by Au thin film (100 nm) to avoid oxidation of electrode over long-term monitoring (45 to 70 h). Remarkably, the data of impedance were converted into a low-dimensional and simple descriptor by the supervised sure independence screening and sparsifying operator (SISSO) to afford quantification of the LWC with a compromise between accuracy and the simplicity and speed of computation, dispensing temperature and moisture values as input data. The prediction accuracy boosted gradually along independent analyses, as expected from a sensor 4.0-based platform. These results suggest the broad applicability of the platform by enabling direct determination of the LWC from leaves at variable climatic conditions. Overall, our findings may help to pave the way for translating “sense–act” technologies into practice toward the on-site and remote investigation of plant drought stress. These platforms can provide key information for aiding efficient data-driven management and guiding decision-making steps.
Audience Take-Away:
- The public will be able to learn how to address common issues within the emerging field of wearable sensors in plants. This provides a practical solution with various proof of concepts, offering a platform that can be used to assist in precision agriculture, material toxicity studies, evaluation of new agricultural fertilizers and pesticides, effects of pathogens, or any other variable correlated with plant water content in real-time and continuously for long periods.
- Furthermore, the platform offers solutions for scalable manufacturing of wearable sensors in a simple and robust manner, including adhesion, sensitivity, low-noise electrical contact to sensing pads, and robustness in variable environments, subjected to real climatic changes. It resolves and simplifies hardware implementations by using machine learning, providing a simplified "sample-to-answer" platform.
- Additionally, we provide a novel study using X-ray nanoprobes by Synchrotron radiation to evaluate the biocompatibility of the devices in the plant's physiological functions over a long period.
