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This is a big step in DNA computing," says Joanne Macdonald, Ph.D., a
virologist at Columbia University's Department of Medicine. Macdonald
led the research team that developed MAYA-II (Molecular Array of YES
and AND logic gates) ¯ a "computer" whose circuits consist of DNA
instead of silicon. She likens the significance of the advance to the
development of the earliest silicon chips. "The study shows that
large-scale DNA computers are possible."
"These DNA computers won't compete with silicon computing in terms of
speed, but their advantage is that they can be used in fluids, such as
a sample of blood or in the body, and make decisions at the level of a
single cell," says the researcher, whose work is funded by the
National Science Foundation. Her main collaborators in this study were
Milan Stojanovic, of Columbia University, and Darko Stefanovic, of the
University of New Mexico.
Macdonald is currently using the technology to improve disease
diagnostics for West Nile Virus by building a device to quickly and
accurately distinguish between various viral strains and hopes to use
similar techniques to detect new strains of bird flu. In the future,
she suggests that DNA computers could conceivably be implanted in the
body to both diagnose and kill cancer cells or monitor and treat
diabetes by dispensing insulin when needed.
Scientists have tried for years to build computers out of DNA (deoxyribonucleic
acid), nature's chemical blueprint for life. But getting nano-sized
pieces of DNA to act as electrical circuits capable of problem-solving
like their silicon counterparts has remained a major challenge.
In a series of laboratory demonstrations over a two-year period,
Macdonald and her associates showcased the computer's potential by
engaging MAYA-II in a complete game of tic-tac-toe against human
opponents, winning every time except in the rare event of a tie. Shown
in the foreground of the picture above is a cell-culture plate
containing pieces of DNA that code for possible "moves"; a display
screen (background) shows that the computer (red squares) has won the
game against its human opponent (blue).
Composed of more than 100 DNA circuits, MAYA-II is quadruple the size
of its predecessor, MAYA-I, a similar DNA-based computer developed by
the research team three-years ago. With limited moves, the first MAYA
could only play an incomplete game of tic-tac-toe, the researcher says.
The experimental device looks nothing like today's high-tech gaming
consoles. MAYA-II consists of nine cell-culture wells arranged in a
pattern that resembles a tic-tac-toe grid. Each well contains a
solution of DNA material that is coded with "red" or "green"
fluorescent dye.
The computer always makes the first move by activating the center
well. Instead of using buttons or joysticks, a human player makes a "move"
by adding a DNA sequence corresponding to their move in the eight
remaining wells. The well chosen for the move by the human player
responds by fluorescing green, indicating a match to the player's DNA
input. The move also triggers the computer to make a strategic
counter-move in one of the remaining wells, which fluoresces red. The
game play continues until the computer eventually wins, as it is
pre-programmed to do, Macdonald says. Each move takes about 30 minutes,
she says.
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