Microscopic glass ribbons provide molecular labels. (Materials Science).

A new type of barcode is too small to see with the naked eye, yet it holds big promise for biomedical research, law enforcement, and everyday life, say researchers.

The fluorescent tagging devices are short glass ribbons just 100 micrometers long and 20 [micro]m wide. They contain stripes reminiscent of the black-and-white barcodes on milk cartons or cereal boxes, but these new barcodes tag large biomolecules, such as DNA. The labels become visible under a microscope when they're hit with a wavelength of light that makes them fluoresce.

Other researchers have created molecular tags from fluorescing particles called quantum dots (SN: 7/7/01, p. 7) or tiny metallic bars overlaid with a sequence of precious-metal stripes, including silver and gold ones (SN: 10/6/01, p. 212). In contrast, the new barcodes are made of glass segments fused into ribbons. Each segment contains small amounts of ions of relatively rare metals, such as dysprosium, thulium, and cerium, which fluoresce in different colors.

Theoretically, the barcodes can be made in more than 100 billion patterns, says Matthew J. Dejneka of Corning in Corning, N.Y. Dejneka, Joydeep Lahiri, and their company colleagues describe the barcodes and their use in tagging genes in the Jan. 21 Proceedings of the National Academy of Sciences.

In addition to labeling biologically interesting molecules, the barcodes could serve as signatures that identify, say, a factory where a specific explosive was made or the paint from a car involved in a hit-and-run accident. They could also serve as invisible badges of authenticity for designer clothing or inks on paper currency, the researchers suggest.--J.G.