Low-cost tool detects bacteria in food in two hours

A sensitive and reliable bacteria-detecting chip that can determine the bacterial load of foods, beverages or water in under two hours is being patented by University of Massachusetts Amherst researchers.

This detection method is claimed to be able to detect as few as 100 bacteria cells per 1 mL of solution, whereas typically other rapid methods claim a sensitivity of 10,000 cells/mL.

The standard method for culturing bacteria from food samples, aerobic plate count (APC), takes two days. Some other methods are faster, but they are not very sensitive or reliable because ingredients in the food can interfere with them.

Food scientists Lili He and Lynne McLandsborough and their students, particularly Brooke Pearson, at the University of Massachusetts Amherst developed the two-step method that has a chemical and then an optical stage.

The first step in the new test for bacteria detection is to collect a sample of water, juice or mashed vegetable leaf and place the chemical-based detection chip in with the sample.

To overcome the food interference problem, the researchers designed the UMass Amherst chip to attract bacteria only, not sugars, fats or proteins in the food or dirt. These food compounds can be washed away with a high-pH buffer, leaving only bacteria for visual counting with a light microscope or a smartphone microscope and app.

The chip, used with a light microscope for optical detection, relies on a ‘capture molecule’, 3-mercaptophenylboronic acid (3-MBPA) that attracts and binds to any bacteria. The chemical detection method, surface-enhanced Raman spectroscopy (SERS), relies on silver nanoparticles.

The optical detection method has also been adapted for possible home use via a smartphone microscope adapter that is widely available online for about $30.