Ouicker gene test developed

Monday, September 11th 2000, 12:00 am
By: News On 6

WASHINGTON (AP) — Genetic testing may take hours, instead of days, and be performed in a doctor's office, instead of at a distant lab, with the use of a new gene identification technique developed at Northwestern University.

Researchers report Friday in the journal Science that the technique uses tiny gold beads and a modified photo developing solution to highlight the presence and density of DNA in a test specimen.

The new technique reads the results using a simple photo scanner costing less than $100, said Chad A. Mirkin, a co-author of the study. The most widely used current DNA testing technique requires a $60,000 microscope, he said.

``Once this system is developed, it may be possible for a doctor to do DNA testing in his office, or for soldiers in the field to do tests to identify biological weapons,'' said Mirkin.

Just as do the current test methods, the new technique starts with DNA chips, glass slides imbedded with strands of synthesized DNA.

The slide is placed in a solution containing the test specimen and target DNA in the specimen binds to the DNA strands on the slide.

Mirkin said the new element in the technique is the use of gold beads a nanometer in diameter. A nanometer is one-billionth of a meter. The width of a human hair is about 100 nanometers.

The gold beads are covered with about 200 strands of DNA. When they are spilled over the DNA slide, the beads match up and cling to the corresponding DNA in the specimen.

Mirkin said the slide is then immersed in a photographic solution. Silver ions in the solution bond with the gold and form black beads of metallic silver that may be 100,000 times bigger than the gold beads.

The whole slide is then put onto a photo scanner. The silver beads, which mark where there has been a DNA match, show up as gray to black dots. The darkness of the dot shows the amount of target DNA present in the specimen, said Mirkin.

Mirkin said the technique is about 100 times more sensitive than current methods and is able to detect as few as 60 molecules of DNA. To achieve that sensitivity, current DNA tests require that the DNA detected be amplified by a laboratory process.

The new DNA test is still in the early stages of development, said Mirkin, but eventually it could be used to genetically identify diseases — from cancer to AIDS — and to detect gene mutations.

On the battlefield, he said, the technique could be used to identify biological warfare agents, such as anthrax, so that soldiers could quickly be given the appropriate drugs.