North Carolina State University researchers led by Zheng li have developed a patch that the plant they can be “worn” to continually monitor for disease or other disruptions, such as crop damage or extreme heat.
A green health sensor
We have created a wearable sensor that monitors plant stress and disease in a non-invasive way by measuring the volatile organic compounds (VOCs) emitted by plants
Qingshan Wei, co-author of the research. Assistant Professor of Chemical and Biomolecular Engineering at NC State University.
Current testing methods for stress or crop disease involve taking plant tissue samples and conducting laboratory analyzes.
However, this only provides growers with one measurement: the time lag between sampling and test results makes it difficult to read.
Different crops, different frequencies
Crops emit different combinations of VOCs under different circumstances. By targeting VOCs relevant to specific plant diseases or stresses, sensors can alert users to specific problems.
“Our technology continuously monitors VOC emissions from the plant, without harming the plant,” says Wei. “The prototype we demonstrated stores this tracking data, but future versions will transmit the data wirelessly. What we have developed allows growers to identify problems in the field – they shouldn't have to wait to receive test results from a laboratory.”
How are “green” patches made?
The rectangular patches are 30 millimeters long and made of a flexible material containing graphene-based sensors and flexible silver nanowires. The sensors are coated with various chemical ligands that respond to the presence of VOCs specific to different crops.
This allows the system to detect and measure VOCs in the gases emitted by the plant's leaves.
The researchers tested a prototype of the device on tomato plants. The prototype was set up to monitor two types of stress: physical damage to the plant and infection with P. infestans, the pathogen that causes downy mildew in tomatoes.
The system detected changes associated with the physical damage of the crops within one to three hours, depending on how close the damage was to the patch site.
Things improved and to be improved
Detecting the presence of P. infestans took longer. The technology didn't detect changes in VOC emissions until three to four days after the researchers inoculated the tomato plants.
“This is not much faster than the onset of visual symptoms of downy mildew disease,” Wei says. “However, the crop monitoring system means that growers do not have to rely on detecting minimal visual symptoms. Continuous monitoring would allow growers to identify plant diseases as quickly as possible, helping them limit the spread of the disease."
The green patch prototypes are already able to detect 13 different VOCs of as many crops with high precision.
Patched crops, treated crops
It is important to note that the materials have a rather low cost. If production increases, this technology will become profitable. A practical solution to such a problem requires very low costs.
The next step for “crop saver” patches? Researchers are currently working on the next generation that can monitor temperature, humidity and other environmental variables, in addition to VOCs. And as mentioned, future versions will be solar powered and capable of wireless data transfer.
