The idea of using DNA molecules -- the material genes are made of -- to perform computations is not new; scientists have been working on it for over a decade. DNA has the ability to store much more data than conventional silicon-based computers, as well as the potential to perform calculations in a biological environment -- inside a live cell, for example. But while the technology holds much promise, it is still limited in terms of the ability to control when and where particular computations occur.

Dr. Alex Deiters, associate professor of chemistry at NC State, developed a method for controlling a logic gate within a DNA-based computing system. Logic gates are the means by which computers "compute," as sets of them are combined in different ways to enable the computer to ultimately perform tasks like addition or subtraction. In DNA computing, these gates are created by combining different strands of DNA, rather than by a series of transistors. The drawback is that DNA computation events normally take place in a test tube, where the sequence of computation events cannot be easily controlled with spatial and temporal resolution. So while DNA logic gates can and do work, no one can tell them when or where to work, making it difficult to create sequences of computational events.

In a paper published in the Journal of the American Chemical Society, Deiters addressed the control problem by making portions of the input strands of DNA logic gates photoactivatable, or controllable by ultraviolet (UV) light. The process is known as photocaging. Deiters successfully photocaged several different nucleotides on a DNA logic gate known as an AND gate. When UV light was applied to the gate, it was activated and completed its computational event, showing that photoactivatable logic gates offer an effective solution to the "when and where" issues of DNA-based logic gate control.

Deiters hopes that using light to control DNA logic gates will give researchers the ability not only to create more complicated, sequential DNA computations, but also to create interfaces between silicon and DNA-based computers.

"Since the DNA gates are activated by light, it should be possible to trigger a DNA computation event by converting electrical impulses from a silicon-based computer into light, allowing the interaction of electrical circuits and biological systems," Deiters says. "Being able to control these DNA events both temporally and spatially gives us a variety of new ways to program DNA computers."

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