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Red Alert Means Infection Detection

Silicon chips in bandages could warn of bacteria

FRIDAY, Nov. 16, 2001 (HealthDayNews) -- The bandage wrapped around your wound may one day be the early warning system for infection, say scientists.

Silicon sensors the size of grains of sand could be embedded in bandages to alert doctors to harmful bacteria, including the deadly blood infection called sepsis, allowing quicker treatment.

The idea comes from chemists and electrical and computer engineers at the University of Rochester's Center for Future Health in Rochester, N.Y. They've developed a biological sensor that turns red when exposed to a certain family of disease-causing bacteria. The tiny device is described in the Nov. 28 issue of the Journal of the American Chemical Society.

Bacteria are either gram-negative -- with thin cell walls -- or gram-positive -- with multi-cell-layered walls. For example, listeria, which causes some food poisoning, is gram positive; Helicobacter pylori, which is involved in ulcers, is gram-negative.

The cell walls of gram-negative bacteria contain substances that have a toxic molecule called lipid A, which causes many of the germs' harmful effects.

Senior author and assistant professor of chemistry Benjamin Miller says the sensor is a silicon wafer similar to those in computers and other electronic devices. The red tinged-wafer has pores, and when the pores become smaller, the color intensifies.

Miller and his team created a molecule, called tetratryptophan ter-cycle pentane (TWTCP), and put it on the wafer to spark the reaction. When the wafer meets gram-negative bacteria, lipid A attaches to TWTCP, reducing the size of the pores and turning the sensor red.

Gram-positive bacteria don't react to TWTCP, so doctors would know immediately what kind of bacteria they're dealing with when the sensors turn red. This will make tailoring antibiotic treatment easier, says Miller.

Theoretically, some other molecules could trigger the sensor, says Miller. "We haven't analyzed every possible substance, but so far … we have yet to get a false-positive signal off the device."

Because the human eye could miss the subtle color change on a tiny wafer, Miller says the sensor will use wireless communication to send its reaction to a simple-to-use device. "Basically, you want a Band-Aid that's going to call you up and say, 'Hey, you're infected'."

Ideally, he says the sensor and other computerized systems could ultimately tell you whether an infection is worth seeing a doctor about.

Eric Anslyn, professor of chemistry and biochemistry at the University of Texas, in Austin, says the sensor could have medical and commercial applications. "It has the potential to be part of a practical diagnostic device," he says.

Miller says the wafer bandages are still experimental but could be ready to test on people in about six months. He says the sensors could be incorporated into bandages in three to five years.

Beyond bandages, he says the same technology could be used to test for bacterial blood infections in the next year or two.

Miller's team is working on a similar test to identify specific gram-positive bacteria. "Obviously, what you'd like to know is … if it's simple, run-of the-mill Escherichia coli, or if it's salmonella or typhus or plague bacteria? We're approaching all of that now," he says.

What To Do

Check these images of common microbes at Cells Alive! or learn about them at the Microbe Zoo.

And if you don't mind wading through some technical jargon, MicroBioNet provides an overview of gram-negative bacteria.

SOURCES: Interviews with Benjamin L. Miller, Ph.D., assistant professor, department of chemistry, University of Rochester, N.Y.; Eric V. Anslyn, Ph.D., professor, department of chemistry and biochemistry, College of Natural Sciences, University of Texas, Austin; Nov. 28, 2001, Journal of the American Chemical Society.
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