In a move sure to confound grocery and convenience store checkers the world over, intrepid chemists have fashioned microscopic bar code rods just a few thousandths of a millimeter long. Really, these striped metal cylinders should make it easier for researchers to scan small samples for the presence of many different biological molecules at once.

Scientists from Pennsylvania State University and SurroMed, Inc., of California, publishing in todays Science, report that they constructed these tiny bar codes by layering metals such as gold, silver and nickel one on top of another in various orders. Because some metals reflect more light than others at certain wavelengths, the rods appear as bands of varying intensity when viewed under the correct light. The authors prepared striped particles from 50 nanometers to about 10 micrometers in length, made from up to five different metals and 13 stripes. With that many stripes, a rod composed of three different metals could take on almost a million distinct patterns.

Bar code rods coated in antibodies or nucleic acids were able to differentiate between proteins from humans and rabbits, and detect the presence or absence of a specific DNA sequence. This NanobarcodesTM technology, owned by SurroMed, could be used to scan for many different molecules at once: a distinct rod would probe for each target. Existing techniques for scanning large numbers of biological molecules rely on fluorescent compounds that come in just a few colors. "The number of uniquely identifiable particles that could be prepared by previous methods was quite limited," says Michael Natan of SurroMed, one of the authors. "With Nanobarcodes, we saw an opportunity to fabricate an essentially unlimited number of codes.