Nano Bar Codes Illuminate Viruses

Medical Device & Diagnostic Industry Magazine
MDDI Article Index

Originally Published MDDI August 2005

R&D Digest



Maria Fontanazza

Using an alternative form of DNA and a fluorescence device, researchers have designed a nano bar code that can be used to identify deadly viruses and bacteria. The technology could help with a number of diagnostic tasks.

The nano bar codes produce colors under an ultraviolet light, which are viewed with a computer scanner or a fluorescent light microscope. They aren't actual bar codes, however. They are fluorescently tagged DNA scaffolds that have precise color ratios. “It's likely that by using these nano bar codes coupled with a flow cytometer or a fluorescence microscope, we could identify different cells, pathogens, or viruses,” says Dan Luo, assistant professor of biological engineering at Cornell University (Ithaca, NY). “One of the beauties of this technology is that it's nanosized, and we can do a lot of things at the nanoscale. It's a platform technology that should be easily extended to the clinical arena.”

Applications could include drug discovery and cell biology for research and development. In diagnostics, the technology could spur development of a more practical way to detect multiple pathogens or cell types in blood samples. The group at Cornell is working toward developing a portable detection device.

It could also complement DNA microarray technology. At a nanoscale level, it may be able to bring detection inside cells or tissue to identify different cell communities without destroying neighboring information.

“In the case of real black-and-white bar codes, the detection is based on the precise two-color patterning, or arrangement, of bars,” says Luo. “We use two fluorescent colors: red and green. The detection is based on the precise arrangement of the colors that gives rise to precise ratios.”

The technology can be used with currently available equipment. Indeed, any equipment—even a digital camera—that can sense or determine the fluorescence's intensity is suitable.

When developing the bar code technology, the researchers decided to use DNA differently—generically rather than genetically. “DNA carries all the genetic information,” says Luo. “In our lab, we purposely completely ignored the DNA's genetic role, and instead used the DNA as a scaffold molecule for a generic purpose. You can almost think of using DNA as a plastic molecule, or as polymers.”

The Cornell team manipulated DNA at the nanoscale level and made it

tree-shaped. Each branch can be precisely and flexibly attached to the different fluorescence sides. “That's the key technology,” says Luo. “No other molecule, other than our DNA, can be used for this purpose.”

The antibodies or binding molecules are attached to a loose end of the DNA. Molecules containing fluorescent dye are attached to the other ends. The color-coded probes are then able to tag molecules of interest.

The team tested the technology with samples that had combinations of anthrax, E. coli, and tularemia bacteria; and ebola and SARS viruses. The color codes were able to differentiate a number of different pathogens at the same time. “Another important aspect is that we can detect more than two types of molecules by different ratios of only two colors, rather than by different colors,” says Luo.

Further testing the technology will include using real samples from patients or real targets, says Luo.

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