"Our approach to this problem has been to think of bacteria as simply micron-sized chemical factories whose exhaust is not regulated by the EPA," Suslick said. "Our technology is now well-proven for detecting and distinguishing among different chemical odorants, so applying it to bacteria was not much of a stretch."
The artificial nose is an array of 36 cross-reactive pigment dots that change color when they sense chemicals in the air. The researchers spread blood samples on Petri dishes of a standard growth gel, attached an array to the inside of the lid of each dish, then inverted the dishes onto an ordinary flatbed scanner. Every 30 minutes, they scanned the arrays and recorded the color changes in each dot. The pattern of color change over time is unique to each bacterium.
"The progression of the pattern change is part of the diagnosis of which bacteria it is," Suslick said. "It's like time-lapse photography. You're not looking just at a single frame, you're looking at the motion of the frames over time."
In only a few hours, the array not only confirms the presence of bacteria, but identifies a specific species and strain. It even can recognize antibiotic resistance a key factor in treatment decisions.
In the paper, the researchers showed that they could identify 10 of the most common disease-causing bacteria, including the hard-to-kill hospital infection methicillin-resistant Staphylococcus aureus (MRSA), with 98.8 percent accuracy. However, Suslick believes the array could be used to diagnose a much wider variety of infections.
"We don't have an upper limit. We haven't yet found any bacteria that we can't detect and distinguish from other bacteria," he said. "We picked out a sampling of human pathogenic bacteria as a starting point."
Given their broad sensitivity, the chemical-sensing arrays also could enable breath diagnosis for a number of conditions. Medical researchers
|Contact: Liz Ahlberg|
University of Illinois at Urbana-Champaign