“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.