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Enjoy your meal
06 October 2001
From New Scientist Print Edition.
Catherine Zandonella, San Francisco

Enlarge Figure 1

Want to know if that dodgy takeaway you bought last night gave you food poisoning? Or was it your lunchtime fish and chips? A clever gadget no bigger than a personal stereo will not only take the guesswork out of the task but also give you a rapid answer.

While the gadget, called ImmunoFlow, will at first be used by food-processing companies, it is so small and light that its inventors ultimately envisage health inspectors delivering on-the-spot justice to restaurateurs trading in spoilt chicken or buggy burgers.

Unlike today's tests, which can take many days, ImmunoFlow should do the job in 15 to 30 minutes. Those saved hours could be critical when investigating an outbreak, says inventor Bart Weimer, a microbiologist at Utah State University in Logan.

"We can now detect bacteria more easily and with better sensitivity than existing commercial tests," says Weimer. ImmunoFlow is so sensitive it can detect Salmonella, Listeria and E. coli O157—even when there are only 100 cells per millilitre.

At the moment, when food inspectors investigate a report of tainted food, they place the offending morsel in a sterile container and take it to a lab for analysis. It takes at least 24 hours for any bugs in the sample to grow on a plate. Sometimes it's seven days before they get an answer.

With the new device, investigators simply pour a smidgen of the suspect food or drink directly into the ImmunoFlow's testing chamber (see Graphic). Solid food has to be pulverised first with a bit of water or buffer solution. A battery-operated pump pushes the sample into the testing chamber.

Inside the chamber are hundreds of glass beads, each coated with millions of antibodies that stick to the kind of bacteria you are testing for, say Salmonella. Previous antibody-based tests lacked the sensitivity of ImmunoFlow, says Weimer, because they relied on the bacteria diffusing through a paper membrane covered with antibodies. But bacteria are big and bulky, so they diffuse slowly and incompletely, which makes the tests less sensitive. The pump in the ImmunoFlow forces the liquid through the beads so the beads don't get clogged. The investigator then adds another set of antibodies labelled with a luminescent marker that will bind to any antibody-bacterium complexes trapped in the chamber, giving off a telltale glow.

You can't spot the glow without plugging the ImmunoFlow into a small machine called a photon counter. Right now, the photon counter is as big as a PC, but Weimer's new company, Biomatrix Solutions, is aiming to make smaller, portable versions. He hopes to begin marketing ImmunoFlow next May.

Eventually, when the photon-reader is small enough,the gadget could be used in the home to test meat or milk that has been sitting around in fridge for a few days. "A rapid test such as this could decrease the number of illnesses and deaths due to food-borne bacteria," says Caroline Smith de Waal of the Center for Science in the Public Interest, a nutrition and food safety advocacy group. "We need to monitor food much more regularly than is being done today."

From issue 2311 of New Scientist magazine, 06 October 2001, page 20

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