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Le er Bugs
When designing experiments, scientists don’t usually
consider what kids might like for their birthdays, but
it seems Manuel Palacios and DavidWalt of Tu s Uni-
versity have arrived at the perfect present (were it at all
appropriate for children). Forget the Acme spy kit—these
researchers have discovered how tomake invisible ink
out of germs. Using bacteria that they geneticallymodi-
fied to light up in different colors, they built a simple
code (e.g., red plus green equals the le er “m”) and laid
out the bacteria in order on a special piece of paper. The
technology could be used for secret watermarks to, say,
protect shipments of high-value pharmaceutical drugs
from thieves. Here’s how they did it.
BY JACQUELINE DETWILER
MEDFORD, MASS.
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Specialty research suppliers sell genes for jelly-
fish proteins that glow blue, green, red, orange
or yellowwhen exposed to fluorescent light.
Palacios andWalt ordered a bunch and attached
them to a common bacteria, then tested them to
see which were the brightest.
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To better hide the secret missives, Palacios and
Walt made some bacteria antibiotic-resistant.
To read themessage, the receivers grew it, then
doused it in ampicillin before shining the light on
it. The ampicillin killed off all the extra glowing
bacteria, leaving only themessage behind.
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The scientists used the bacteria to lay out a
color-codedmessage on “paper”made of nitro-
cellulose.When themessage’s intended receivers
got it, all they had to dowas press it into bacteria
food (no, not your son’s socks—it’s called agar)
tomake it grow. After two days, they shined a
fluorescent light on it and the colors appeared.
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FEBRUARY 2012
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