Purdue team demonstrates portable system in field for first time
WEST LAFAYETTE, Indiana – Purdue University researchers are introducing a new biosensor technology to the agriculture industry, inspired by advances made during the COVID-19 pandemic.
This system produced 100% accurate results within one hour of sample collection on a commercial fresh produce farm.
“The approach we used is using a fecal indicator called Bacteroidales as a risk indicator,” said Mohit Verma, associate professor of agricultural and biological engineering at Purdue. Verma and his team of nine postdoctoral researchers, graduate and undergraduate students published their findings in the journal Biosensors and Bioelectronics. Agritech, a startup company where Verma serves as chief technology officer, is licensing the technology Purdue Innovates Office of Technology Commercialization.
“The goal is to predict what risks may be present in fresh produce operations from nearby animals or other wildlife,” Verma said. Typically, this is done by measuring pathogens. If pathogens are present on the crop, it is discarded. But detecting pathogens at low levels, in compliance with regulatory requirements governing products with a short shelf life, presents challenges.
The technology used by Verma is called loop-mediated isothermal amplification (LAMP). The team has implemented it on innovative, paper-based devices for quick results for agricultural uses. Earlier, Verma's team had developed these tests for bovine respiratory disease and COVID-19.
“To our knowledge, this work represents the first demonstration of a portable LAMP testing platform implemented on a fresh produce farm,” the co-authors wrote in their journal article.
The new paper also refines previous results published in the journal Food Microbiology by Verma and his colleagues, led by lead author Xiangshan Wang, who earned a doctorate in agricultural and biological engineering from Purdue University this year.
Bacteroidales is a fecal organism found in pigs, poultry, and cattle. Most foodborne pathogens associated with fresh produce, including E. coli and Salmonella, originate in the intestines.
The Purdue team tested the system on a commercial lettuce farm in Salinas, California, and on a field next to the Purdue Animal Sciences Research and Education Center in West Lafayette, Indiana. Microbial samples were collected from plastic flags placed in the test area.
Verma's experiments involved collecting bioaerosol samples for a week from small flags made of plastic sheets. The experiments compared testing in the field and in the lab. All the flags were brought to the lab for quantitative polymerase chain reaction testing. “This allows you to measure the level of Bacteroidales and therefore fecal contamination,” Verma said.
But with the new assay kit, which includes a drop dispenser, paper-based device, and a heating imager, growers can perform the entire process in the field. After clearing the collection flag, they insert a drop dispenser into it that is preloaded with liquid to deliver a specific volume.
The liquid is poured into paper devices containing the compounds needed to detect DNA in the samples. The paper device then goes into a heating imager. An hour later, the device reveals how much of Bacteriodales is present. The assay provides quantitative test results that confirm what growers, after visual inspection, often intuitively suspect is happening in their fields.
The field test results matched the lab results 100%. This included samples with very low or very high levels of contamination. It is challenging to completely change the level of contamination in field testing, but it is part of the ongoing work, Verma said.
The field test lacked samples with a moderate range of contamination, which would have revealed most of the anomalies. Even then, the assay could detect only three copies of Bacteroidales DNA per square centimeter. Verma estimates that tests with the full range of contamination would achieve a concordance of more than 90% with the laboratory test.
A low level of Bacteroidales indicates a low-risk area. A high level indicates a need for caution. A high level of contamination would be 1,000 copies of DNA per square centimeter found on the test pad, one copy of which corresponds to one cell of any broad class of bacteria. A low level would be 10 copies per square centimeter.
“The biggest limitation is that we don't yet know what these numbers mean,” Verma said. “What's in between? Where do we draw the line? That's part of the ongoing work,” he added.
Lead author Wang and Simardeep Kaur, a PhD student in the Department of Agricultural and Biological Engineering, developed the assay and paper-based device and conducted the field testing. Co-authors from the Weldon School of Biomedical Engineering and the Elmore Family School of Electrical and Computer Engineering developed the heating imager. Other co-authors assisted with field test preparations and device optimization.
This work demonstrates the Verma group's ability to go from developing something new in the lab to testing it in the field. “Not everyone can do this, and you certainly can't do it alone. The list of authors indicates that,” Verma said.
Funding for the project came from the Center for Produce Safety, the California Department of Food and Agriculture, and the U.S. Department of Agriculture Agricultural Marketing Service. Verma informed Purdue Innovates about the innovation to the Office of Technology Commercialization, which has applied for a patent to protect the intellectual property. OTC issued a license for the technology to Verma's company, Krishi. Krishi is currently raising capital for commercialization.
About Purdue University
Purdue University is a public research institution that demonstrates excellence at scale. Ranked among the top 10 public universities and with two colleges in the top four in the United States, Purdue pursues and disseminates knowledge with a quality and scale that is second to none. More than 105,000 students study at Purdue in a variety of ways and locations, with nearly 50,000 of those students studying in person at the West Lafayette campus. Committed to affordability and accessibility, Purdue's main campus has kept tuition stable for 13 consecutive years. See how Purdue doesn't stop in its relentless pursuit of the next big leap – including its first comprehensive urban campus in Indianapolis, the Mitchell E. Daniels, Jr. School of Business, the Purdue Compute and the One Health initiative – at https://www.purdue.edu/president/strategic-initiatives,
Author: Steve Koppes
media Contact: Devin Revere, [email protected]
Source: Mohit Verma, [email protected]
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