New DNA sensors offer quick cost-effective food detection

The sensors, developed by a team of researchers at the Universitat Autònoma de Barcelona (UAB), have the same size and thickness as a fingernail and reduce the time needed to identify DNA chains to several minutes or a few hours, depending on each chain.

The development comes on the back of increasing research into food detection at the molecular level. Nanotechnology, science involving the use of materials the size of millionths of a millimetre, has thrown up new possibilities in monitoring never before imagined, and this latest discovery has the potential to dramatically increase food safety at every stage of the supply chain.

Food safety and the development of early warning systems is a growing area of study given the emphasis on food safety and the perceived threat of terrorism. In addition, food manufacturers and retailers are increasingly aware that a contaminated batch of food could lead to, at best, a product recall and at worst closure and legal proceedings.

What makes this discovery so significant therefore is the possibility that these sensors could cost as much as a pregnancy test kit once mass production begins.

The researchers Salvador Alegret, Manuel del Valle and Maria Isabel Pividori, all of whom are members of the sensors and biosensors group at the UAB​'s department of chemistry, developed the new sensors based on their experience in research with electrochemical sensors. These can identify a substance by chemically interacting with it and converting this interaction into an electrical current that they measure.

To detect DNA, the new miniaturised electrochemical genosensors have a probe containing DNA fragments that complement the DNA they aim to detect. For example, to detect Salmonella in a sample of mayonnaise, the probe has fragments of the type of DNA that complements that found in a group of genes that identify the bacteria.

When the probe is submerged into the mayonnaise, some of the DNA fragments from the bacterial cells join the complementing fragments from the probe, creating a measurable electrical current. The sensor converts this current into a signal that can be seen by the person controlling the tests, making him aware there are bacteria.

Also, because the sensors are very small and easy to manipulate, it is possible to assemble a set of sensors that can collect data simultaneously and deduce information about the bacteria such as which strain caused the foodborne illness.

This type of analysis already takes place in laboratories, but until now the experimental measures needed were not suitable for in situ analysis. By using the new sensors developed by UAB scientists, the time taken to identify the source of infection for Legionella would decrease from two days, as is currently the case using organic production techniques, to just thirty minutes.

In trials developed with the support of the UAB's Department of Genetics and Microbiology, the new sensors have enabled Salmonella to be identified in four and a half hours, compared to three to five days using the traditional microbiological methods. This method for identifying bacteria could also be used to detect other infectious agents such as Campylobacter and Listeria.

"The next step is to mass-produce the sensors,"​ said Salvador Alegret, the director of research. "Mass production will allow costs to be reduced and the product to become as widely available as pregnancy test kits we can buy at the local pharmacy."​