Handheld sensor detects pathogens within 10 minutes
10 minutes whether their products are laden with Escherichia coli
or listeria -- before they are shipped out of the plant.
Increasing regulatory emphasis on food safety in plants and the cost of recalls has spurred food companies to seek faster ways of detecting pathogens.
Raj Mutharasan, an engineer at Drexel University in Philadelphia, Pennsylvania, has developed what he says is a cheap, quick and simple detector that just about anyone can use.
"It will be as easy to use as a thermometer, giving a result in 10 minutes," Mutharasan stated in New Scientist yesterday.
Detecting the bug in plants is a slow process that involves removing whole batches of foodstuffs from production lines while cultures are grown or DNA amplified. Normal laboratory tests can take 24 hours or more
The device works by detecting how the mass of a few E. coli cells changes the vibration of a miniature glass beam. Mutharasan's prototype sensor is made up of a sliver of glass five millimetres long and one millimetre wide.
The glass is fixed at one end and has a layer of piezoelectric ceramic called lead zirconate titanate (PZT) glued to the other. The glass sliver is coated with antibodies to E. coli 0157:H7, the strain that causes food borne illness.
An alternating voltage applied to the piezoelectric layer makes it expand and contract, causing the tiny sliver to vibrate. The vibration is greatest at the sliver's resonant frequency, and this can be detected by measuring the voltage across the PZT generated by the reverse piezoelectric effect, as it peaks at the resonant frequency.
Changes in the resonant frequency as E. coli cells bind to the antibodies provide a measure of the concentration of the pathogen.
To make sure only E. coli cells sit on the sliver, the testing procedure takes place in moving fluid. To test beef broth, for example, a fraction of a millilitre of the liquid is sloshed back and forth over the sensor.
"The sensitivity is already very high," Mutharasan stated. "We can detect E. coli at a concentration of four cells per millilitre of sample."
The sensitivity of the sensor, which can also detect other pathogens such as listeria, has attracted interest from US government departments.
The Department of Agriculture is developing the sensor further with the Drexel team, with the National Institutes of Health and the Environmental Protection Agency part-funding the work.
In the US, about 60 people a year die from E. coli, while 73,000 are infected with pathogenic strains.
