When farmers find sickly plants in their crops, it's important that they find out which malady is responsible, as quickly as possible. New microneedle technology could help, paving the way for a handheld device that would provide the answer within minutes, right in the field.

In cases where it's not immediately obvious which illness is afflicting a plant, samples taken from that plant are often analyzed to see which disease-causing organism's DNA is present. Before that DNA can be identified, though, it first has to be isolated from the sample material, typically via a multi-step process known as CTAB (cetyltrimethylammonium bromide) extraction. Performed in a lab, this involves grinding plant tissue, adding organic solvents, and placing the mixture in a centrifuge – it also takes three to four hours to carry out.

In an effort to develop a quicker, easier alternative, scientists at North Carolina State University created a postage stamp-sized patch made from an inexpensive polymer, which is covered on one side with hundreds of tiny needles.

Measuring just 0.8-mm long, each of those needles pierce into the plant as the patch is held against its surface. After a few seconds, the patch is peeled off and rinsed with an aqueous buffer solution. DNA-containing genetic material gathered from the plant by the needles gets washed off as this happens, ending up in a sterile container along with the buffer.

The whole process takes only about a minute, after which the extracted DNA still has to be identified in a lab – for now. And although a small amount of impurities do end up being present in the buffer, they haven't proven to be problematic, as the technology has already been successfully used to extract and identify the DNA of organisms causing late blight disease in tomato plants.

"DNA extraction has been a significant hurdle to the development of on-site testing tools," says Asst. Prof. Qingshan Wei, co-corresponding author of a paper on the study. "We are now moving forward 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."

The paper was recently published in the journal ACS Nano.

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