Plant pathogen sensor uses smartphone to detect diseases
“All plants release VOCs as they ‘breathe,'” says Qingshan Wei, an assistant professor of chemical and biomolecular engineering and corresponding author of a paper on the project, “but the type and concentration of those VOCs changes when a plant is diseased. Each disease has its own signature profile of VOCs. So, by measuring the type and concentration of VOCs being released by the plant, you can determine whether a plant is diseased and – if it is diseased – which disease it has.”
Current plant disease identification techniques rely on molecular assays, which must be performed in a lab setting and take hours to produce results. Getting a sample to the lab, where the sample may have to wait to be tested, can delay disease identification by days or weeks.
“Our technology,” says says Jean Ristaino, William Neal Reynolds Distinguished Professor of Plant Pathology at NC State, co-author of the paper and director of the NC State’s Emerging Plant Disease and Global Food Security cluster, “will help farmers identify diseases more quickly, so they can limit the spread of the disease and related crop damage. We are now ready to scale up the technology.”
To use the technology a leaf from the relevant plant is placed in a test tube, which is then capped for at least 15 minutes to allow the relevant VOCs to accumulate. After this incubation period, the cap is removed and a narrow, plastic tube is used to pump the VOC-laden air into a “reader” device connected to a smartphone.
The air is pumped into a chamber in the reader that contains a paper strip, which is embedded with an array of chemical reagents that change color when they come into contact with a specific chemical group. By evaluating the resulting color pattern on the strip, users can determine the nature of any plant disease that may be affecting the plant.
“For this technology to work,” says Zheng Li, a postdoctoral researcher at NC State and first author of the paper, “we had to develop reagents that could be embedded in the paper strips. About half of the reagents were off-the-shelf organic dyes, but the other half were gold nanoparticles that we functionalized to respond to specific chemical groups. These functionalized nanoparticles allow us to be more precise in detecting various types of VOCs.”
The researchers say they also had to design and build the reader device, since “there is nothing like it on the market.”
In proof-of-concept testing, the researchers say they demonstrated the device’s ability to detect and classify 10 plant VOCs down to the parts-per-million (ppm) level. They were able to detect the late blight pathogen that caused the Irish famine two days after tomato plants were inoculated with the pathogen.
The technology was also able to distinguish tomato late blight from two other important fungal pathogens that produce similar symptoms on tomato leaves. In addition, say the researchers, they showed they could detect the pathogen Phytophthora infestans in tomato leaves with greater than 95% accuracy.
Looking ahead, the researchers say they are hoping to improve their technology in two areas. First, they would like to automate the pattern analysis using software for the smartphone, making it easier for users to make disease determinations.
Second, they envision the development of customized reader strips designed to measure the VOCs associated with other diseases specific to a given crop. Different crops in different regions face different threats, say the researchers, so paper strips could be developed that are tailored to address those specific concerns.
For more, see “Non-invasive plant disease diagnostics enabled by smartphone-based fingerprinting of leaf volatiles.”
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