Fingernails store personal information

Eugen Leitl eugen at
Wed Jul 6 08:33:00 PDT 2005

At least, here you don't have to lose a whole digit if your biometrics is

Fingernails store personal information

6 July 2005

Japanese researchers are using femtosecond laser pulses to write data into
human fingernails.

Secure optical data storage could soon literally be at your fingertips thanks
to work being carried out in Japan. Yoshio Hayasaki and his colleagues have
discovered that data can be written into a human fingernail by irradiating it
with femtosecond laser pulses. Capacities are said to be up to 5 mega bits
and the stored data lasts for 6 months - the length of time it takes a
fingernail to be completely replaced. (Optics Express 13 4560)

Fingernail storage

"I don't like carrying around a large number of cards, money and papers,"
Hayasaki from Tokushima University told "I think that a key
application will be personal authentication. Data stored in a fingernail can
be used with biometrics, such as fingerprint authentication and intravenous
authentication of the finger."

The team's approach is simple: use a femtosecond laser system to write the
data into the nail and a fluorescence microscope to read it out. The key to
reading the data out is that the nail's fluorescence increases at the point
irradiated by the femtosecond pulses.

Initial experiments were carried out on a small piece of human fingernail
measuring 2 x 2 x 0.4 mm3. The writing system comprises a Ti:Sapphire
oscillator and Ti: Sapphire amplifier. Pulses of less than 100 fs at 800 nm
are then passed through a microscope and focused to three set depths (40, 60
and 80 microns) using an objective lens.

Each "bit" of information has a diameter of 3.1 microns and is written by a
single femtosecond pulse. A motorised stage moves the nail to create a bit
spacing of 5 microns across the nail and a depth of 20 microns between
recording layers.

An optical microscope containing a filtered xenon arc lamp excites the
fluorescence and reads out the data stored at the various depths. "We
regulate the focus with the movement of the microscope objective," explained
Hayasaki. "The distance between the planes is set to prevent cross-talk
between data stored at different depths."

Hayasaki adds that the same fluorescence signal is seen 172 days after

Although the initial experiments have concentrated on small pieces of nail,
the team is now developing a system that can write data to a fingernail which
is still attached to a finger. "We will develop a femtosecond laser
processing system that can record the data at the desired points with
compensation for the movement of a finger," said Hayasaki.

Jacqueline Hewett is technology editor on and Opto & Laser Europe

Eugen* Leitl <a href="">leitl</a>
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