A team of University of Florida researchers has created tiny hybrid particles that can speedily root out even one isolated E. coli bacterium lurking in ground beef or provide a crucial early warning alarm for bacteria used as agents of bioterrorism and for early disease diagnosis.
The study will appear this week in the Proceedings of the National Academy of Sciences.
"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," said Weihong Tan, a UF Research Foundation professor of chemistry and associate director of UF's Center for Research at the Bio/Nano Interface. "Because of these properties, we're able to finish the detection of a single bacterium in 20 minutes."
Bionanotechnology is a new frontier of research that combines two seemingly incompatible materials – the building blocks of life and synthetic structures – at a tiny, molecular-sized scale. Nanotechnology works with objects that are on the order of 1 to 100 nanometers; a nanometer is one-billionth of a meter, about the size of several atoms. When combined with molecular biology, the possible applications of this nano-frontier are widespread and sound like the stuff of science fiction. Scientists currently are designing microscopic "nanobots", bioprobes and biosensors that, once implanted in the human body, could perform a number of medical duties, from delivering drugs to detecting malignant cells.
Tan's compound materials are called "bioconjugated nanoparticles," a prefix-heavy term that highlights their blended nature. "It's a very simple idea," said Tan. He takes antibodies -- molecules used to seek specific types of bacteria -- and attaches, or "conjugates", them to tiny dye-loaded particles.
"A bioconjugated particle is linked to the antibody, which can recognize a specific type of bacterium," Tan said. "Inside this particle, we put many fluorescent dye molecules in such a way that you can generate a very, very high signal." Once a particle finds the bacteria that it's designed to seek, it glows.
Dye-labeled antibodies are commonly used to locate bacteria in a sample, but traditional methods are not very sensitive -- the glow from one antibody-linked dye molecule just isn't easy to see, and that can create potential health risks. "Sometimes one bacterium makes the difference," Tan said.
The secret to the UF team's super-sensitive method is in the sauce: The silica structure they use to bind the antibody-and-dye amalgam together allows each particle to hold thousands of dye molecules, rather than just one, making the fluorescent signal hundreds to thousands of times brighter.
Enhancing the fluorescent signal also eliminates a time-consuming part of the current bacteria detection process. Small amounts of bacteria are difficult to detect and to count how many bacteria are in a sample, scientists often have to "plate" it -- place the sample in a Petri dish and let the bacterial colonies grow for one to a few days before analysis. However, the bioconjugated nanoparticles found a single E. coli bacterium in a sample of ground beef in less than 20 minutes, from start to finish.
A quicker analysis time is not only vital for early disease detection but also will be critical in combating bioterrorism, Tan said. "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." Analyzing a possible bioterrorist agent by traditional means could take days and would involve sealing off the entire area during that time, he said. "Instead, we can come back in 20 minutes and say either this is safe or there is a problem." Chad Mirkin, professor of chemistry at Northwestern University and director of Northwestern's Institute for Nanotechnology, said the new technique looks promising.
"This looks to be a pretty impressive way of detecting bacteria, and the obvious point of impact would be in the food safety industry," Mirkin said. "It looks quite good for pathogen detection in foods, which is a huge issue."
The research team includes former UF scientist Xiaojun Zhao, now an assistant professor at the University of North Dakota; UF graduate student Lisa Hilliard; postdoctoral researchers Shelly John Mechery, Yanping Wang and Rahul Bagwe; and Shouguang Jin, associate professor of molecular genetics and microbiology. The research was funded by the National Science Foundation, the Packard Foundation and the National Institutes of Health.
The team now is working on tailoring the bioconjugated nanoparticles to detect multiple bacteria simultaneously, including health threats E. coli, Salmonella and Bacillus cereus spores, a toxin found in many foods. The ultrasensitive particles can be adapted to detect a wide variety of bacteria used as bioterrorism agents in food, clinical and environmental samples and can be used to detect disease in its earliest stages, Tan said.
"This is really the interface of biological science and nanotechnology," he said. "In situations when the very sensitive detection of bacteria or other biological reagents is the critical issue, I think our technology will have a clear edge."