Wearable sensor supports in-situ and continuous monitoring of plant health in precision agriculture era

Abstract

Plant health is intricately linked to crop quality, food security and agricultural productivity. Obtaining accurate plant health information is of paramount importance in the realm of precision agriculture. Wearable sensors offer an exceptional avenue for investigating plant health status and fundamental plant science, as they enable real-time and continuous in-situ monitoring of physiological biomarkers. However, a comprehensive overview that integrates and critically assesses wearable plant sensors across various facets, including their fundamental elements, classification, design, sensing mechanism, fabrication, characterization and application, remains elusive. In this study, we provide a meticulous description and systematic synthesis of recent research progress in wearable sensor properties, technology and their application in monitoring plant health information. This work endeavours to serve as a guiding resource for the utilization of wearable plant sensors, empowering the advancement of plant health within the precision agriculture paradigm.

Keywords: in‐situ and continuous; monitoring; plant health information; precision agriculture; wearable sensors.

Figure 1

Basic elements and classification of wearable plant sensor. (a) The flexible substrate and sensing material undergoes a serials of processing steps, combined with encapsulation to form the main structure of the sensor. Together with the modification and integration of transduction circuits, a laptop or phone used to collect information could eventually be applied to plant health monitoring. Wearable sensors are structured in three layers, forming a sandwich configuration: the first layer includes substrate material (such as plastic polymer substrate, hydrogel and other substrates), the second layer comprises sensing material (including metal materials, nanomaterials, carbon‐based materials and other conducting polymer materials), the third layer consists of encapsulation materials (including liquid polymer and flexible polymer sheets) and transmission electronics (involving wired or wireless connections); (b) Classification of wearable plant health sensors, organized into three categories based on their functions and application scopes of these monitored physiological parameters on living plants: plant growth sensor, plant microclimate sensor, plant stress sensor. Examples of three types of wearable sensors include a plant growth sensor designed for monitoring fast‐growing fruits/plants (Lee et al., 2022). Copyright © 2022, American Chemical Society.; a multifunctional wearable sensor developed to perceive light illumination, temperature and humidity in plant microclimates (Lu et al., 2020) Copyright © 2020, American Chemical Society; and wearable sensor employed for monitoring plant stress biomarkers or detected objects (VOCs) (Li et al., 2023b) Copyright © 2023 Wiley.

Figure 2

Design & mechanism, and fabrication & characterization of wearable plant sensor. (a) Crucial components in the design of a comprehensive wearable sensor system are depicted, encompassing encapsulation material, sensing material, connection pads, wired or wireless connection sensing circuit, substrate material and data readout platform. The sensing mechanism and electrochemical signals (such as resistance (R), current (I), voltage (V), capacitance (C), impedance (Z) and electrical potential (E)) of wearable plant sensors are influenced by the specific plant detection application. The unique sensing mechanisms result from alterations in chemical (e.g., H₂O, VOCs, pesticides and phytohormones) or physical (e.g., plant growth dimensions) properties between the detected object and the sensing material. (b) A schematic diagram illustrates common fabrication techniques and characterization tools used for wearable plant sensors. These fabrication methods encompass physical approaches (e.g., direct writing, coating, printing, spinning, deposition, etc.) and chemical methods (e.g., cross‐linking). Likewise, common characterization tools include morphology assessment (XRD, XPS, TEM and SEM), optical evaluation (LSCM, FTIR, UV–vis–NIR and Raman), electrical analysis (DLS, EIS, CV and LCR) and more.

Figure 3

Wearable plant sensor for in‐situ monitoring of plant growth. (a) Schematic representation of a plant with its body parts equipped with these sensors. Three main growing sections of testing include stem growth, leaf growth and fruit growth. (b) Wearable sensors of plant intrinsic growth can be based on strain sensors and targeted plant development, improved the sensitivity of growth detection. When the strain sensor detects mechanical stress or strain related to plant growth, it will transmit electrical signals or data to a receiving device or system (Tang et al., 2019). Copyright © 2019 Elsevier. (c) (1) Double network (DN) stretchable strain microfibers are envisioned to be useful in stretchable strain sensors to measuring the growth of bamboo (Kim et al., 2019a). Copyright © 2019 Wiley. (2) Hsu et al. (2021) created an ultra‐thin wearable sensor for aloe leaves, incorporating polyacrylic acid double‐networked with a conductive nanofiller, specifically reduced graphene oxide coated with polyaniline (PAA‐RGO‐PANI) (Hsu et al., 2021). Copyright © 2021 Elsevier. (3) Lee et al. (2022) encapsulated a stretchable strain sensor composed of a poly(ethylene glycol) (PEG) and silver nitrate composite within various elastomers. This sensor exhibited high sensitivity, reliable repeatability and exceptional stability on fruits over several weeks (Lee et al., 2022). Copyright © 2022, American Chemical Society.

Figure 4

Wearable plant sensor for in‐situ monitoring of plant microclimate. (a) Schematic of a plant equipped with a multifunctional wearable sensor for extrinsic microclimate monitoring, and the detection objects included in the plant microclimate encompass humidity of the plant itself and microclimate, temperature of the plant itself and microclimate and light in the microclimate. (b) The sensing mechanism of wearable sensors for monitoring plant extrinsic microclimate: plant intrinsic and extrinsic humidity; plant intrinsic and extrinsic temperature; plant extrinsic light. (c) A humidity sensor utilizing an OCF sensor has been proposed, involving the modulation of humidity‐response functional group concentrations on carbonized textiles for humidity measurement (Yi et al., 2022). Copyright © 2022 Elsevier. A multimodal wearable sensor attached to the lower leaf surface offers continuous monitoring of plant physiology, tracking biochemical and biophysical signals of both the plant and its microenvironment. This integrated sensor platform detects humidity VOCs, and temperature, within a singular framework (Lee et al., 2023). Copyright © 2023, American Association for the Advancement of Science. A ZIS‐based flexible sensor has been introduced, capable of swiftly sensing light illumination (∼4 ms response time) and providing robust and consistent humidity monitoring, a characteristic that remains unparalleled in other reports (Lu et al., 2020). Copyright © 2020, American Chemical Society.

Figure 5

Wearable plant sensor for in‐situ monitoring of plant stress. (a) Schematic of a plant experiencing abiotic and biotic stress (e.g., excessive pesticides, insect pests, weed infestations, pathogens), and plant with the tested objects and biomarker (e.g., pesticide, phytohormone, VOCs) equipped with wearable plant sensors for monitoring plant stresses. (b) Wearable plant sensors can detect the changes of stresses tested objects and biomarkers (pesticides, phytohormones, VOCs and harmful gas molecules are common), and thus altering the electrical signal, then allowing for the detection of the changes of stresses. (c) (1) A wearable non‐enzymatic electrochemical sensor has the potential to detect carbamate and bipyridinium pesticides on agricultural and food sample surfaces (Paschoalin et al., 2022). Copyright © 2022 Elsevier. (2) The suggested IAA sensor demonstrated strong sensitivity and selectivity, finding utility in the in vivo detection of IAA concentrations in soybean seedlings experiencing salt stress (Li et al., 2019a). Copyright © 2019 Elsevier. (3) A wearable electrochemical VOC sensor, created through the electrodeposition method, demonstrates remarkable sensitivity and selectivity as a sensing material. This material was utilized for on‐leaf monitoring of methanol emission from maize (Ibrahim et al., 2022). Copyright © 2022, American Chemical Society.

Figure 6

Current limitations, challenges and prospects of wearable plant sensors. Limited accuracy, sensitivity and stability affected by environment and data interpretation limitations are the main limitations of technology today; limited parameter coverage and spatial resolution limitations are the main limitations of the application. Weight & stretchability, accuracy, sensitivity, lifespan and biocompatibility are the main challenges of wearable plant sensor technology today; Other unknown biomarkers, mass production, real exposure scenarios and safety issues are the main challenges of wearable plant sensor application in agriculture today. Future studies could focus on lightweight, high stretchability & accuracy & sensitivity & biocompatibility, longer lifespan, identifying more biomarkers, more sustainable and safer wearable plant sensors; realizing mass production and low cost, conducting field and real‐world scenarios applications and collaborating with scientists from other fields and ultimately achieving sustainable development in precision agriculture era.