Microneedle plant patches (North Carolina State University)
11 June 2019. A small patch with tiny needles collects DNA from leaves in about one minute, making possible portable devices to detect plant diseases. Researchers from North Carolina State University in Raleigh describe the microneedle patch in the 9 June issue of the journal ACS Nano (paid subscription required).
The team of NC State plant scientists and engineers are seeking faster and easier methods for growers to detect and analyze diseases affecting their crops. Farmers currently use a method called cetyltrimethylammonium bromide, or CTAB, to extract DNA from plant samples. This technique is carried out in the lab with expensive equipment that grinds up specimen samples, then mixes the samples with solvents to extract the DNA for analysis to reveal the presence of disease-causing pathogens. The process takes 3 to 4 hours to return results, according to the authors.
The researchers instead want a fast, simple technique for DNA extraction from plants that growers can use in their fields. “When farmers detect a possible plant disease in the field, such as potato late blight, they want to know what it is right away,” says Qingshan Wei, professor of chemical and biomolecular engineering and one of the project leaders in a university statement. “Rapid detection can be important for addressing plant diseases that spread quickly,”
Their technique uses a disposable polymer patch about the size of a postage stamp with hundreds of needles less than 1 millimeter in length. The patch is applied to a plant’s leaf for a few seconds, and removed and washed in a buffer solution that separates genetic material from the sample. The genetic material is then captured in a separate sterile container for further amplification and analysis. The process takes about 1 minute, and no further purification is needed.
The researchers tested the patch on tomato plant leaves grown in the lab and in the field infected with late blight disease, caused by the fungus Phytophthora infestans, or P. infestans. This fungus affects potatoes as well as tomatoes, and is responsible for the deadly potato famine in Ireland in the 19th century. But because late blight disease can look like other destructive fungi, DNA analysis is often needed to precisely identify the cause.
“The gold standard for disease identification is a molecular assay,” says plant pathology professor and co-project leader Jean Ristaino. “Our new technique is important because you can’t run an amplification or genotyping assay on strains of P. infestans, or any other plant disease, until you’ve extracted DNA from the sample.”
Tests of the patch show the DNA samples extracted from tomato leaves did not quite reach the purity of CTAB samples, but were still sufficient for DNA analysis. Subsequent DNA testing of the samples indicated the presence or absence of P. infestans on the leaves, which was confirmed in all samples by CTAB testing.
“We are now moving forward,” says Wei, “with the goal of creating an integrated, low-cost, field-portable device that can perform every step of the process from taking the sample to identifying the pathogen and reporting the results of an assay.”
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