In-Field Monitoring of Plant Stress with a Low-Cost Electrochemical Sensor

Environmental challenges, like drought, severe temperatures, pests, and diseases, have adverse effects on the growth, development, and yield of plants. Salicylic Acid (SA) serves as a plant hormone responsible for signaling in response to stress, and it plays a crucial role in plants' defense mechanisms against certain types of pathogens. Elevated levels of salicylic acid in plants serve as an indicator of stress. It is essential to monitor and assess plant stress to ensure the well-being and productivity of crops, as well as a steady food supply. The on-site measurement of salicylic acid aids in the early detection and diagnosis of plant stress, enabling prompt actions to reduce harm and sustain crop productivity.<br/><br/>Point-of-care diagnostic technologies have emerged as an advancement in medical analysis and monitoring. These technologies offer a decentralized and cost-effective approach, making accessibility to crucial diagnostic services easier. As a rapid first line of diagnosis, they serve as a frontline defense.<br/><br/>In this work, we introduce an affordable electrochemical tool designed for the purpose of tracking plant stress by detecting Salicylic Acid (SA). The device is equipped with wireless connectivity, allowing it to transmit data to a smartphone via the Bluetooth Low Energy (BLE) protocol.<br/><br/><b>Methods</b><br/>Electrochemical techniques have been used to monitor SA levels. We've utilized laser-induced graphene (LiG) electrodes, a low-cost and scalable 3D porous carbon material created through laser-based polymer-to-graphene conversion, which shows promise for electrochemical sensors.<br/><br/>We've developed an affordable, portable potentiostat to continuously monitor salicylic acid (SA) levels in plants, with the collected data being transmitted to a nearby smartphone via Bluetooth Low Energy technology.<br/><br/><b>Results</b><br/>The ability to efficiently scale the production of LiG electrodes offers a cost-effective method for creating these systems. Examination of these electrodes reveals the formation of a graphene layer on the PI film. Moreover, by optimizing laser machine parameters, we have achieved electrodes that not only consistently reproduce but also exhibit impressive electrochemical capabilities.<br/><br/>Square-wave voltammetry measurements were conducted using the LiG sensors, with varying concentrations of SA in buffer. The peak current value demonstrates a linear relationship with the SA concentration, with a sensitivity of 130.54 µA/mM, and linearity range between 5 µM and 150 µM. The limit of detection is 1.75 µM.<br/><br/><b>Conclusion</b><br/>An affordable device based on laser-induced graphene (LiG) for monitoring plant stress is created, and it is seamlessly integrated with a portable potentiostat. This device enables the detection of salicylic acid, a phytohormone vital for plant stress signaling. The detection is achieved using a 3-electrode LiG design, and our system has successfully demonstrated this capability.