Purdue University researchers have unveiled biosensor technology aimed at transforming agricultural practices by swiftly identifying contamination risks in fresh produce. 

The new system, inspired by COVID-19 testing methods, demonstrated 100 percent accuracy within an hour of in-field sample collection when tested on a commercial fresh produce farm.

“The approach we’ve taken is using a fecal indicator called Bacteroidales as a risk marker,” said Mohit Verma, Purdue’s associate professor of agricultural and biological engineering. The work, documented in the journal Biosensors and Bioelectronics, is licensed through Krishi, a startup where Verma serves as chief technology officer.

Traditionally, risk assessment in fresh produce involves measuring pathogens, which, if detected, lead to crop disposal. However, detecting pathogens at low levels, as required by regulatory standards for products with a short shelf life, presents substantial challenges. Verma’s team’s solution involves using loop-mediated isothermal amplification (LAMP) technology, previously utilized for diagnosing bovine respiratory disease and COVID-19. The innovation lies in implementing LAMP on paper-based devices, enabling rapid, on-site testing for agricultural applications.

The research, conducted on a commercial lettuce farm in Salinas, CA, and near Purdue’s Animal Sciences Research and Education Center in West Lafayette, used plastic flags to collect bioaerosol samples. “That allows you to measure Bacteroidales and therefore the level of fecal contamination,” Verma said. The system’s accuracy was verified by comparing field and laboratory results, with the new assay kit providing growers with immediate, actionable data.

Growers use a drop dispenser, preloaded with liquid, to swab collection flags. The liquid is then dispensed onto paper devices containing compounds necessary for DNA detection. After placing the paper device into a heating imager, the results, available in an hour, reveal the presence and level of Bacteroidales. The technology offers a quantitative measure, confirming suspicions about field contamination and enabling timely interventions.

Despite the system’s promising accuracy, Verma acknowledged the need for further testing across a broader contamination range. Current field tests lacked intermediate contamination samples, which are essential for a comprehensive validation. Nevertheless, the assay detects as few as three copies of Bacteroidales DNA per square centimeter, suggesting high potential for widespread agricultural application.

The research also addresses the challenge of interpreting contamination levels. “We don’t really know what these numbers mean yet,” Verma said. Establishing thresholds for contamination levels is ongoing work, vital for the practical deployment of the technology.

Lead authors Jiangshan Wang and Simerdeep Kaur spearheaded the development of the assays and paper-based devices. The project also involved significant contributions from the Weldon School of Biomedical Engineering and the Elmore Family School of Electrical and Computer Engineering, particularly in developing the heating imager.

This project underscores the Verma group’s capability to transition innovations from the lab to field testing, a feat not easily accomplished. Verma emphasized the collaborative effort, highlighting the extensive list of contributors.

Funding for this 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. The Purdue Innovates Office of Technology Commercialization, which applied for a patent for this technology, has issued a license to Krishi. The startup is currently raising capital to bring the technology to market.

The full study can be found here.

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