Testing crops for diseases currently involves sending plant samples to a lab, which only provides one measurement and takes valuable time before the growers get the results. North Carolina State University (NC State) researchers have developed a tool to provide continuous monitoring for plant diseases and stresses: a wearable patch.

"We've created a wearable sensor that monitors plant stress and disease in a noninvasive way by measuring the volatile organic compounds (VOCs) emitted by plants," said Qingshan Wei, assistant professor of chemical and biomolecular engineering and co-corresponding author of a paper on the work.

Because plants emit different combinations of VOCs depending on environmental conditions, the Plants can wear the patch to monitor continuously for plant diseases or other stresses, such as crop damage or extreme heat. Source: Qingshan Wei, NC State Universityresearchers were able to target the VOCs that indicate a specific disease or stress. The sensors can then alert the growers when any of these conditions is present.

The patch is a 30 mm long, flexible rectangle containing graphene-based sensors and flexible silver nanowire. The sensors are coated with chemical ligands that respond to the presence of specific VOCs, enabling them to detect and measure VOCs in the gases the plants emit through their leaves.

A prototype was set up to monitor for physical damage and infection by a pathogen that causes late blight disease in tomato plants. The system detected VOC changes related to physical damage in one to three hours, depending on the distance from the damage to the patch. Detection of the pathogen, P. infestans, took three to four days from the time the researchers inoculated the plants.

"This is not markedly faster than the appearance of visual symptoms of late blight disease," Wei said. "However, the monitoring system means growers don't have to rely on detecting minute visual symptoms. Continuous monitoring would allow growers to identify plant diseases as quickly as possible, helping them limit the spread of the disease."

The prototypes can accurately detect 13 different plant VOCs so users can customize their sensor array to focus on the stresses and diseases that are most relevant to them. A next-generation patch is now under development to monitor temperature, humidity and other environmental variables. Future versions of the sensor described in the journal Matter will be solar-powered and able to transfer data wirelessly.