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Researchers in Japan have managed to carve tiny numbers and pictures into a fingernail, in the form of microscopic dots burnt into the nail by laser.

The team has only managed the feat on nail clippings so far, but they hope the process could one day be used to securely carry information on live fingertips. It might even replace credit cards, they suggest, although you'd have to get your information carved in every six months or so as the nail grows out.

Yoshio Hayasaki of the University of Tokushima and colleagues say a single fingernail could accommodate something like 800 kilobytes of data. That won't provide room for a high-resolution photo, but would be enough to store basic identification information.

Hayasaki and his team achieve the feat by using a laser that delivers very short pulses of infrared light onto a finely focussed spot, they report in Optics Express1. The researchers think the energy unravels keratin molecules in the nail, which makes the molecules more fluorescent. When the nail is illuminated with blue laser light to excite fluorescence, recorded dots appear brighter than the material surrounding them, allowing the information to be read out under a microscope.

A single fingernail could hold 800 kilobytes of data.

Because it is possible to adjust the depth of the writing laser's focal spot inside the nail, they say, several layers of information can be superimposed within a single slab.

But writing and reading with a live subject would be tricky, says the team, because the spots are just 3 micrometres across. Slight, involuntary movements of the subject's finger during carving would ruin the effect. They are working on a way to compensate for this movement.

"It's interesting work, no question," says Peter Török, a specialist in optical data storage at Imperial College in London. But he cautions that, quite aside from the matter of having to replenish the data every six months or so, there are some substantial obstacles to turning the approach into a practical technology.

"If your nail gets too warm, that could cause problems," says Török. Heating can uncoil keratin too, he points out.

And the system might not be so secure. "It would be very simple to forge the information," says Török. "You wouldn't need a lot of technology to do that."

Perhaps the system would be of more use to people who want to surreptitiously move information from one place to another. So although credit cards are unlikely to be replaced any time soon, spies and government agents may prove customers for this technology.

http://www.nature.com/news/2005/050718/full/050718-3.html