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Thursday, September 30, 1999 Published at 11:09 GMT 12:09 UK


The lean mean gene machine

Current gene chips use technology adapted from silicon chips

A digital movie projector has been used to create a new, cheaper gene chip which crams half a million tiny mirrors on to a centimetre square chip.

An unlikely alliance of molecular biologists and semiconductor engineers at the University of Wisconsin, Madison, made the breakthrough, which promises to allow far more biologists to harness the power of DNA chips.

[ image: The new chip uses digital movie projection technology]
The new chip uses digital movie projection technology
These are used to scour huge chunks of animal and plant genomes for genes that may cause disease or biological phenomena such as ageing. Genes involved in the ageing of mice were recently discovered by a different group of Wisconsin scientists using this technology.

At the moment gene chips cost about $2,500 off the shelf but customised versions containing DNA from specific organisms or tissues can take months to make and cost as much as $12,000.

The time and expense of manufacture is due to the way the chip works. Chunks of DNA are built up by adding one base (A, C, T or G) at a time. Which base joins on is determined by a beam of light falling on particular parts of the chip, while the rest of it is shaded by a stencil-like mask.

However, the complexity of the molecules required to answer specific genomic questions is such that up to 80 different masks can be needed, making the chip too difficult and expensive to manufacture in most laboratories.

No smoke, lots of mirrors

The new chip does away with the need for masks by using 480,000 tiny aluminium mirrors to direct the light to the right places.

The researchers used Texas Instrument's Digital Micromirror Device (DMD), which has already been used to project the latest Star Wars film to moviegoers in Los Angeles. The DMD has a 600 by 800 array of 16-micron mirrors. This can be used to illuminate nearly half a million pixels on a chip just 10 by 14 millimetres.

In tests, the chips precisely detected three types of mutation in two genes from the thale cress plant.

Alan Blanchard and Stephen Friend, at Rosetta Inpharmatics, Washington State, believe the new gene chip could allow many biologists access to the analytical technique who could not have afforded it before.

Commenting on the work published in Nature Biotechnology, they said: "It is clear that for the scientists wanting to do [gene chip] experiments, unlike the moviegoers of Los Angeles, the price of admission will soon be falling."

However, they also raise concerns that must be overcome if the technology is to be successful. For example, it takes 100 cycles of the chip to build a 25-base molecule. But the efficiency of the process is 95%, meaning only 28% of the final molecules will be synthesised as desired.

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