When Mike
Burkart and James La Clair play their modified CD player they hear
molecules instead of music. Burkart, a biochemistry
professor, and La Clair, a visiting scholar, have
developed a way to use a conventional
CD player as a diagnostic tool. And the error message is the key.
Except
for home pregnancy and blood glucose tests for diabetics, looking
for molecules in the body has been the domain of medical
laboratories. These tests are often expensive, which means that
they have been
virtually unavailable for people in the developing world.
Since
scientific laboratories often rely on laser light to detect molecules,
it made sense to Burkart and La Clair to design a way
to detect molecules using the most ubiquitous
laser on the planet—the CD player.
“
The CD is by far the most common media format in our society on
which to store and read information,” says La Clair, who
initially developed and patented the technique. “It’s
portable, you can drop it on the floor and it doesn’t break.
It’s
easy to mass produce. And it’s inexpensive.”
Anything
adhering to a CD surface tends to interfere with a laser’s
ability to read digital data burned onto the CD. While that is
usually considered a drawback, the UCSD researchers exploited this
characteristic to detect molecules.
The typical CD consists of
a layer of metal sandwiched between a layer of plastic and a protective
lacquer coating. When a CD is burned, a laser creates pits in the
metal layer. A CD player uses a laser
to
translate the series of pits and intervening smooth surface into
the corresponding zeros and ones that make up the bits of digital
information.
In order to screen molecules, the researchers took
a CD encoded with digital data, and enhanced the chemical reactivity
of the
plastic on the readable surface. They
then added molecules to the empty inkwells of an inkjet printer
cartridge and used the printer to “print” the molecules
to specific locations on the CD.
Certain proteins or other large
molecules discovered in a blood sample can indicate the presence
of disease. Medical technicians can therefore use specific molecules
on the surface of a CD to “go fishing” for certain
proteins in a blood sample. This is possible because some proteins only bind to specific target molecules, like a key that
only fits in a certain lock. Wherever a protein attaches to the
CD, the laser in a CD player will detect an error in the digital
code, allowing a computer program to determine which proteins are
present in the sample.
“
That’s the novelty of this,” Burkart points out. “We
are actually using the error to get our effect. James has even
done this using CDs with music, like Beethoven’s Fifth Symphony
and you can actually hear the errors.”
A few bugs need to
be ironed out before the technique can be used to accurately quantify
the amount of a given protein in solution.
In the meantime, the researchers hope that others will customize
this technology in a variety of ways. Eventually it could lead
to a wide range of inexpensive new diagnostic kits. Compared to
the
$100,000 price tag for a fluorescent protein chip reader, Burkart
points out, a CD player costs as little as $25.
“
In theory,” says La Clair, “anyone who has a computer
with a CD drive could do medical tests in their own home.” |
