Researchers in Professor Graham Cooks group at Purdue University, USA, have shown that the new mass spectrometric technique known as desorption electrospray ionisation (DESI) can be used to detect and accurately identify bacteria in minutes rather than hours, removing the need for lengthy and laborious pretreatment steps that can take hours.
"We can determine the subspecies and glean other information by looking at the pattern of chemicals making up the pathogen, a sort of fingerprint revealed by mass spectrometry," Cooks said.
"Conventional wisdom says quick methods such as ours will not be highly chemically or biologically specific, but we have proven that this technique is extremely accurate."
If combined with the portable mass spectrometers also under development at Purdue university the technique could lead to the creation of a new class of fast and accurate detectors for monitoring food safety, health care and homeland security.
Such a system would rapidly alert employees in the food and healthcare industries to the presence of pathogens as well as allowing security personnel with new tools for screening suspicious suitcases and packages. The technique could also be used to analyse air samples in public places such as hospitals and airports.
The technique can detect less than a nanogram (a billionth of a gram) of bacteria, which equates to approximately 5000 bacterium. Yishu Song, lead author of the paper published in the first issue of Chemical Communications in 2007 told LabTechnologist.com that detection limits could be even lower.
The study was able to detect and identify living, untreated bacteria including Escherichia coli and Salmonella typhimurium which can both cause fatal infections in humans.
DESI mass spectrometry involves spraying a sample with positively charged water and methanol molecules which transfer the extra proton to molecules in the sample turning them into positively charged ions themselves. The ionised molecules are then sucked into the vacuum chamber of the spectrometer where the masses of the ions are measured.
When used with bacterial samples, fatty acids and lipids contained in the bacteria are ionised and on analysis exhibit characteristic "mass fingerprints" that correlate to specific bacteria. The study reports that not only can the technique determine the species of a bacterium, it can also determine the subspecies.
According to Song studies are currently underway to replicate the results using standard sized mass spectrometers equipped with the prototype DESI OmniSpray Ion source manufactured by Prosolia, USA, on their MINI 10 mass spectrometer. The MINI 10 is a small portable mass spectrometer that weighs about ten kilograms (one thirtieth of a normal spectrometer) and fits in a shoebox. Critically, it can also run on batteries, allowing it to be used anywhere.
The technique has previously been shown by Cooks' group to be able to help surgeons detect the boundaries of cancerous growths as well as to detect and identify residues from explosives.