Researchers in South Korea may have come across a novel and effective idea to tackle foods tainted with Salmonella bacteria. What looks like a disk actually contains six separate microfluidic slices that work together to provide DNA extraction, amplification, and detection in less than 30 minutes instead of days and a full-blown lab typically required for Salmonella detection.

A computer (PC) controls the motorized rotor that spins the disc, a laser that heats up chambers inside the disc, and a strobe light and camera (CCD) that snap pictures of the disc’s readout strip. Credit: Analytical Chemistry

Salmonella causes an estimated 1.2 million illnesses and 450 deaths in the U.S. each year. While the FDA runs periodic tests on food, especially imports, some contaminated food slips by because there aren’t enough resources to check foods quite as thoroughly as possible. The standard test involves growing cultures in the lab and then checking for strains of microbes. This takes days, requires expensive machinery and trained staff.

The Salmonella Disk

Yoon-Kyoung Cho of Ulsan National Institute of Science & Technology believes shes and her team have devised a method that might dramatically sped up the process and save a lot of money. The disk is essentially a microfluidic chip comprised of six identical slices, each capable of performing the same test. A network of channels and chambers run through each slice  that carry out individual steps in the pathogen detection process. After a sample is added to the center of the device, the rotation of the disc forces the solution outward into the channels of each slice.

For their demonstration, the South Korean researchers spiked milk and butter with known amounts of Salmonella enteritidis colonies. Before loading either sample in the salmonella disk detector, the researchers first concentrated the bacteria by capturing them with magnetic beads coated in anti-Salmonella antibodies.

The beads were loaded in a machinery with rotating disk and laser, which was fired on the salmonella detector disk. The samples flow from chamber to chamber, expanded by the heat of the laser, until it reaches the DNA amplification chamber. Here DNA is amplified via a reaction called recombinase polymerase amplification using primers specific to a known Salmonella gene. The primers are decorated with two molecules that allow for detection of the DNA using reagents.

Eventually, the DNA hits a detection strip where the reagents mixed with the DNA cause a visible band of color to form. The researchers found they could detect as few as 100 colony-forming units of Salmonella in milk and 10 in butter. This isn’t perfect, as even one cell can cause disease, but it’s a promising first step in this direction.

Findings were reported in the journal Analytical Chemistry.