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.