A new tool could detect bacteria in foods and liquids much faster than current methods. Credit: The University of Massachusetts Amherst

A new, low cost tool could help cooks using fresh fruits and vegetables and aid workers responding to natural disasters, by rapidly detecting bacteria in foods and liquids.

Scientists from the University of Massachusetts at Amherst have developed the new tool to detect bacteria in water or food that includes both an optical and chemical component.

“Most people around the world cook their vegetables before eating, but here in the U.S. more and more people like to eat these foods raw,” food scientist Lili He said in a statement. “This gave us the idea that a quick test that can be done at home would be a good idea.

“Microbial contamination is an important research topic right now,” she added. “It has been a problem for a long time, but it is now the number one concern for food safety in the U.S.”

The researchers designed a sensitive and reliable bacteria-detecting chip that can test whether foods, including fresh spinach or apple juice, carry a bacterial load.

A light microscope is used for optical detection with the chip, which also relies on 3-mercaptophenylboronic acid (3-MBPA)—which scientists dubbed a “capture molecule”—to attract and bind any bacteria. 

The researchers then used a chemical detection method called surface-enhanced Raman spectroscopy (SERS), which relies on silver nanoparticles.

Last year, the researchers adapted the optical detection method for possible home use with a smartphone microscope adapter that is widely available to consumers for about $30.

The standard method for culturing bacteria in food samples—called aerobic plate count (APC)—can take two days for results.

“There are some others that are faster, but they are not very sensitive or reliable because ingredients in the food can interfere with them,” He said. “We show in our most recent paper that our method is both sensitive and reliable and it can give you results in less than two hours.”

The scientists developed the chip to address food interference problems by only attracting bacteria and not sugars, fats and proteins found in food or dirt. The food compounds can be washed away with a high-pH buffer, leaving only bacteria for visual counting with the smart phone microscope and app.

This method allows the detection of as few as 100 bacteria cells per one milliliter of solution, while other rapid methods have a sensitive of 10,000 cells.

The study was published in Food Microbiology.