Secret Message Hidden in Dot of DNA

By PETER SVENSSON, AP - June 12 '99

Updating a Nazi spy trick used during World War II, scientists have devised a way of hiding a coded message in a dot of human DNA.  The technique wouldn't be of much use to secret agents because it is a cumbersome way of sending a message.  It is little more than a neat trick that exploits the enormous capacity of DNA to hold information.

Nazi spies sent messages by reducing them photographically to a so-called microdot. The dot was then pasted over a period at the end of a sentence in an innocent-looking letter, which was dropped in the mail.

In Thursday's issue of the journal Nature, researchers led by molecular biologist Carter Bancroft at the Mount Sinai School of Medicine in New York describe how they made - and mailed - a microdot that contained a secret message hidden amid millions of strands of DNA.

Bancroft likened it to a page from the ``Where's Waldo'' children's books, where Waldo is hidden in a large, detailed drawing of lots of people.

DNA is shaped like a twisted ladder, with four kinds of rungs, called bases. The scientists built a DNA strand in which different combinations of bases represented the letters of their message.  At either end of the strand they put sequences of bases that would serve as the key to finding the strand. The strand was one three-thousandths the width of a human hair in length.  The scientists then chopped the entire DNA of a human cell into pieces of about the same length, and mixed them with the message strand.

They soaked the mixture into paper with a period printed on it, cut out the period and pasted it onto a letter. They mailed the letter to themselves to prove that the DNA could survive the rigors of the U.S. mail.

When the letter arrived, they extracted the DNA, multiplied millions of times the strand containing the message, and read its contents. The message they chose for their test was perhaps the most famous secret of the microdot era: ``June 6 invasion: Normandy.''

Without knowing the key, it would be practically impossible to find the message among the 3 million or so similar strands of DNA.  ``This is definitely an intriguing idea,'' said Anne Condon, a computer scientist at the University of Wisconsin-Madison. ``It exploits one of the great advantages of DNA, which is that you can have a huge amount of information in a tiny volume.'' Conventional computers would not be of much use in reading a DNA microdot, Condon said. Instead, it might require advances in DNA computing, the fledgling field of making DNA strands do math, she said.

As for any practical applications, you would need a biochemical lab both to write and to read the messages.  ``At this point of cryptography, it's more of intellectual interest,'' Bancroft said.

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