Using sound to detect bacteria in water

Current techniques for analysing water in the field can take as long as 24 hours to complete, according to Bart Lipkens of Western New England College in Springfield, Massachusetts and his colleagues at Physical Sciences in Andover, Ma.

They are working on an alternative technology that uses sound waves to accelerate the process.

"The goal of our project is to speed up the detection of bacteria in water supplies," said Lipkens. "We're developing a first order trigger, an alarm that maybe there's something in the water that warrants further investigation."

Lipkens has created a device that quickly gathers bacterial spores from running water using acoustical radiation force. It broadcasts waves of ultrasound into the liquid, exerting a pressure on the bacteria that pushes it into a collection pocket. In previous work, Lipkens used this technique to successfully separate polystyrene beads from water.

The device can draw in 15% of the bacterial cells from the water in a single pass. When the flow is shut off, the bacteria settle and can then be transferred to another apparatus for identification. Compared to existing methods, this procedure is quick.

Bacillus cereus, the species of bacteria used in this experiment, is about a micron in diameter and harmless. But its properties are very similar to many types of bacteria that would be harmful in drinking water.

"We think we would ultimately get the same results with harmful bacteria," said Lipkens.