Arizona State University scientists developed microfluidic chip identifies E. coli O157:H7

Newly developed microfluidic chip to sort good germs from bad

6:07 AM, 30th November 2013
Arizona State University  research news on E. coli O157:H7
Shown are generic E. coli and bacteria populations isolated on a micro device.

ARIZONA, US: Arizona State University scientists have developed a microfluidic chip, which can sort good germs from bad. Human intestine is home to about 100 trillion bacteria. That’s more than the number of cells that comprise the entire human body. Armies of bacteria sneak into our bodies the moment we are born. For the most part, these bacteria are industrious and friendly. Some of them are even beneficial, helping with digestion and producing vitamins. A few miscreants, though, will kill us if we let them stay.

The differences between the harmless and harmful are very small. E. coli, for instance, lives in the average person’s intestines. They go about their business causing no trouble whatsoever. However, one particular strain of E. coli, O157:H7, causes about 2,000 hospitalizations and 60 deaths in the US every year. The differences between this strain and others are detectable only at the molecular level.

Research team led by Mark A Hayes, Professor, Arizona State University have developed a new device that could significantly speed up the identification process for harmful bacteria and other microorganisms. The team hopes to create handheld, battery-operated devices that could deliver answers in minutes, instead of days.

Identification takes place within a microscopically small channel in a chip made from glass or silicone polymer. The microchannel features saw-tooth shapes that allow researchers to sort and concentrate microbes based on their unique electrical properties.

The phenomenon that makes this work is called dielectrophoresis, which involves an applied voltage that exerts force upon the bacteria. This force acts like a coin-sorter, causing bacteria to become trapped at different points along the channel. Where they stop, and at what voltage, depends on their molecular and electrical properties.

Using this approach, Hayes’s team including graduate student, Paul V Jones, has separated extremely similar bacteria - pathogenic and nonpathogenic strains within the single species, E. coli.

“The fact that we can distinguish such similar bacteria has significant implications for doctors and health officials. Scientists have struggled to find ways to rapidly identify bacteria. E. coli O157:H7 is very similar in size and shape to other subtypes of the bacteria. But unlike many of the others it has the ability to produce shiga-like toxin, a protein that breaks down blood vessel walls in the digestive tract,” said Hayes.

Fortunately, all of these bacterial strains also possess subtle, but telltale differences in the proteins and other molecules that they express on their surface. According to Professor Hayes, dielectrophoresis is well suited to probe these phenotypic differences.

The researchers used an ordinary strain of E. coli along with two pathogenic varieties. They injected the cells into each channel and simply applied voltage to drive the cells downstream. The geometric features of the channel shape the electric field, creating regions of different intensity. This field creates the dielectrophoretic force that allows some cells to pass, while trapping others based on their phenotype.

So far, the device has only been used to test pure cultures of bacteria, but they hope soon to test complex mixtures of particles that are found in nature or the human body. The next step is to create cheap, portable devices that would enable point-of-care or field based analysis. Such a device would require no time-consuming culturing or other tests, which would allow rapid response to disease or contamination, hopefully saving lives.

© Arizona State University News

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