Researchers Develop a Low-Cost, Reusable, Quick-Sensing Stress Monitor — For Plants

Researchers from Iowa State University have developed a wearable stress sensor for plants — using microneedles to pick up changes that could require intervention before a plant's condition deteriorates.

"We can achieve direct measurements in under a minute for less than a dollar per test," says corresponding author Liang Dong of the team's sensor, which is applied the leaf of a living plant without the need to take or prepare samples for lab analysis. "This breakthrough will significantly streamline analysis, making it practical for farmers to use our patch sensor for real-time disease crop monitoring."

The sensor is designed to detect plant stress in the form of excess hydrogen peroxide — the traditional detection of which required manual sample collection and the removal of plant parts, or the use of fluorescence detectors that can mistake changes in chlorophyll levels for stress. The team's approach is different: a standalone patch that adheres to the underside of leaves, leaving the top free to continue photosynthesis.

The sensor's microneedles are coated in a hydrogel enzyme mixture which converts hydrogen peroxide into electrical current — which can then be measured, and used to infer a plant's stress levels. Tested on both soybean and tobacco plants, the team found its sensor produced more electrical current on bacteria-infected plants than healthy ones, returned a hydrogen peroxide measurement that agreed with existing methods, but did so in just one minute — and could measure levels lower than previous attempts. Better still, each patch can be reused up to nine times before the microneedles lose their edge.

"This sensor technology offers a portable, on-site solution for H₂O₂ measurement," the researchers conclude, "eliminating the need for the intricate and time-consuming sample preparation required by conventional methods such as histological staining. The sensor demonstrated rapid detection capabilities, with a response time of around one minute for in situ measurements. Additionally, this sensor exhibited significant sensitivity, a low LOD [Limit of Detection], a wide dynamic range, and high portability, outperforming other H2O2 electrochemical sensors in the literature."

The team's work has been published in the journal ACS Sensors under open-access terms. "Our next step," Dong says, "is to refine the technology and enhance its reusability."