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Posted: 10/14/2004 9:43:04 AM EDT

Nanoparticles Tag Dangerous Bacteria in Minutes
Fast and super-sensitive system could lead to safer food and water, early disease diagnosis and better bioterrorism prevention
By Gabe Romain
Betterhumans Staff
10/12/2004 4:11 PM

Credit: Proceedings of the National Academy of Sciences
Glowing success: A new system uses dye-filled nanoparticles to attach to and detect deadly bacteria such as this Escherichia coli O157:H7 (above: fluorescent image; below: scanning electron microscope image)

A new fast and super-sensitive nanoparticle-based bacterial detection system has been developed that could lead to safer food and water, early disease detection and new prevention strategies for defending against bioterrorism.

The system, developed by researcher Weihong Tan and colleagues at the University of Florida in Gainesville, uses nanoparticles containing fluorescent dyes to identify dangerous bacteria.

"Our focus is the development of a bionanotechnology that combines the strengths of nanotechnology and biochemistry to generate a new type of 'bionanomaterial,' which has some unique properties," says Tan. "Because of these properties, we're able to finish the detection of a single bacterium in 20 minutes."

Difficult detection

Rapid and sensitive identification of bacteria is extremely important. Harmful bacteria can cause sickness, disease and death. Certain strains of the bacterium Escherichia coli (E. Coli), for example, can cause widespread illness if they get into the food supply.

Exposure to a rare strain called E. Coli O157:H7—often by consuming undercooked or contaminated ground beef—can cause bloody diarrhea and kidney failure. Several of the reported outbreaks of E. coli O157:H7 have even led to death, especially in cases involving children and the elderly, say the researchers.

Current methods for detecting bacteria, such as culturing and polymerase chain reaction, are limited because they're either too slow or not sensitive enough. Recently, many attempts have been made to improve the sensitivity of bacteria detection, however, rapidly detecting bacteria with single-cell resolution has proven difficult.

"Revolutionary tool"

For their study, Tan and colleagues created "bioconjugated nanoparticles," what Tan calls "a very simple idea." The nanoparticles consist of antibodies—molecules that recognize specific microorganisms—attached to particles containing fluorescent dye. The researchers used a silica structure to bind the antibodies and dye in such a way that allows each particle to hold thousands of dye molecules.

For this study, Tan and colleagues used antibodies specific to the E. Coli O157:H7 strain. When mixed with a ground beef sample containing the strain, the antibodies and nanoparticles attached themselves to the bacteria's surface, providing a fluorescent signal a thousand times brighter than traditional detection tools.

The nanoparticles enabled significant amplification of the signal of interest because of the many dye molecules inside each nanoparticle. Using the new method, the researchers were able to detect a single bacterium in less than 20 minutes. In addition, many samples can be analyzed simultaneously for high-throughput bioanalysis of multiple pathogens.

"The ultimate power of the bioconjugated nanoparticles will emerge as a revolutionary tool for ultrasensitive detection of disease markers as well as infectious agents," the researchers write. "Indeed, by using the dye-doped nanoparticles as fluorescent markers, highly sensitive target detection has been achieved, opening the possibility for the fabrication of truly smart bioprobes and biosensors for rapid and ultrasensitive determination of bacterium samples."

Life and death decisions

The researchers say that the speed with which their detection system can work could make it useful for fighting bioterrorism. Traditional detection systems could involve days of work and the isolation of an area, while the new system could give an answer about a sample's danger in minutes.

"In situations when there is life and death, when you have to make a decision very quickly, our technology will really give you the quick decision," says Tan.

The researchers are now working on developing their nanoparticles to detect many bacteria simultaneously and are targeting the food toxins Salmonella and Bacillus cereus.

The research is reported in the Proceedings of the National Academy of Sciences (read abstract).

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