Bacteria-binding chip speeds up testing of raw foods

US scientists have developed a two-stage process that quickly detects whether contamination is lurking in uncooked food.

Including larger quantities of raw fruit and vegetables in your diet might be beneficial to long-term health, but avoiding cooking increases the chances that an enjoyable meal could be followed by a nasty bout of food poisoning.

Scientists at the University of Massachusetts Amherst are aiming to reduce that risk with a rapid and low-cost method for detecting bacteria during food preparation that they say could also be used by aid workers in the field responding to natural disasters.

UMA food scientist Lili He says that microbial contamination has been a problem for a long time, but it is now “the number one concern” for food safety in the US. Most people around the world cook their vegetables before eating, but here in the US more and more people like to eat these foods raw,” she said. “This gave us the idea that a quick test that can be done at home would be a good idea.

The two-part technique is claimed to be both sensitive and reliable, and capable of providing results in under two hours compared with two days for the standard lab-based approach of culturing bacteria from food samples. It can detect contamination at levels as low as 100 bacteria cells per 1 millilitre of solution, compared to a sensitivity of 10,000 cells for other rapid methods.

The first step is based on optical detection. A chip incorporating ‘capture molecules’ of 3-mercaptophenylboronic acid (3-MBPA) that attract and bind to bacteria but not sugars, fats or proteins is added to a sample of water, juice or mashed vegetable leaf before being analysed with a light microscope. A separate chemical detection step uses surface-enhanced Raman spectroscopy and relies on silver nanoparticles.

The optical detection process has already been adapted for home use with a smartphone microscope adapter that is widely available online for about $30 and an app developed by a high school student in He's food science laboratory.

The new techniques, which have been reported in the Royal Society of Chemistry journal Analytical Methods and are the subject of a paper due to be published in Food Microbiology, are now being patented. "This is just the beginning of the work," said He, who hopes to receive more funding to continue.

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