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Analytical Chemistry

Bacteria In Water Monitored Nonstop

Bioanalysis: Device could serve as early warning system

by Stu Borman
September 15, 2014 | A version of this story appeared in Volume 92, Issue 37

A schematic showing several hamster-like objects swimming down a chanell through an area with little tags. As they pass through, they pick up the tags.
Credit: Adapted from Anal. Chem.
Voltage (+V) and pressure applied across a microfluidic channel concentrate fluorescently labeled antimicrobial peptides in a narrow band (crescent). When a water sample containing bacteria flows through the band, the peptides stick to the bacteria, which are detected downstream. Red and blue circles are electrodes.

Bacterial contamination of drinking water is a worldwide problem that each year causes millions of people to become sick and possibly face hospitalization and even death. Yet tests that could alert people to dangerous bacteria in drinking water remain difficult to carry out, in both developed and resource-limited countries.

Currently, scientists use immunoassays or try to grow bacteria collected from water samples to test for contamination. These approaches are time-consuming and require preparation of discrete samples and transport to laboratories for analysis by trained technicians.

Nanotechnologist Ortal Schwartz and mechanical engineer Moran Bercovici at Technion—Israel Institute of Technology have developed a method that could sidestep some of these problems (Anal. Chem. 2014, DOI: 10.1021/ac5017776). It uses microfluidic chips and the charge-based separation technique isotachophoresis to measure bacteria in water continuously, instead of in discrete samples, without the need for sample preparation or lab analysis.

If further developed, such a device could make it possible to conveniently monitor contamination in water sources, water treatment plants, or homes in real time. Potential applications include public health monitoring, medical diagnostics, and food safety.

In the new technique, a voltage applied across the length of a microfluidic channel concentrates fluorescently labeled antimicrobial peptides in a confined region. These short, positively charged peptides are produced by many organisms, from bacteria to mammals, to defend against microbial infection.

Pressure combined with isotachophoresis force water samples to flow through the channel and past the focused fluorescent peptides, which bind to any bacteria present. The tagged bacteria are then detected downstream. “They look like little balls of fire flying through the channel,” Bercovici tells C&EN.

The approach is at a proof-of-concept stage. The group hopes to boost water throughput and bacterial sensitivity, extend the device’s continuous operation time, and use antibodies instead of antimicrobial peptides to enable detection of specific bacterial species or strains. “We have submitted a provisional patent and hope to commercialize the idea,” Bercovici says.

“There is still work to be done, but with optimization this could be a truly unique platform for continuous bacteria monitoring,” comments capillary and microchip electroseparations specialist Michael Breadmore of the University of Tasmania, in Australia.

Waterborne-pathogen monitoring expert Helen Bridle of Heriot-Watt University, in Scotland, agrees that further development is needed but says that even the current version “might not be too far off” from becoming a viable early-warning detection system for bacterial water contamination. She notes that the greatest risk to water supplies, apart from deliberate adulteration, is fecal contamination from sewage, and in such cases there might be enough bacteria present to be detected by the new technique.



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