All of the complex computations in
today’s state-of-the-art computers are performed by hundreds of millions of
simple hardware bits known as logic gates. Each logic gate is made of a
few transistors connected in very specific ways. Using the 0s and 1s of binary
code as their inputs, logic gates perform logical operations at blinding
speed.
For example, if both of the logic inputs
that a logic gate receives are “1,” it will produce the output for “AND.”
Other combinations of 0s and 1s yield “OR,” “NOT,” and so on.
This approach has worked well with logic
gates made of silicon. However, great potential exists for a quantum leap in
performance when we start making logic gates from short strands of DNA.
As Columbia University chemist Milan
Stojanovic and University of New Mexico computer scientist Darko Stefanovic
explained recently in Scientific American,1 a new method for using molecules for
computing and for autonomous decision making suggests that this quantum leap
may be closer than most people believe.
Stojanovic and Stefanovic are devising a
system for making “smart” agents, or drugs that could be injected into a
patient’s bloodstream, assess the person’s medical condition, and then decide
independently how to respond. If successful, a doctor could inject a smart
agent into a diabetic that would constantly monitor the person’s blood glucose
levels and, when necessary, release insulin.
The new approach follows previous efforts
over the past 15 years by other researchers to make logic gates from molecules.
In 1993, A. Prasanna de Silva and other
researchers at Queen’s University Belfast constructed logic gates from small
molecules. These molecules served as an “AND” logic gate because they would
light up only if both hydrogen ions and sodium ions bound to them.
Four years later, J. Fraser Stoddart and
a team of researchers at Birmingham University created an “OR” gate that worked
when a molecule lit up if it detected one of the inputs, but not both. The
inputs in that study were hydrogen ions and amines.
Then, in 1995, Gerald F. Joyce invented a
new method at the Scripps Research Institute for using strands of DNA...
