When anthrax-laden letters contaminated a U.S. Senate building and a postal facility in Washington, D.C., last fall, it often took days to test samples. A new biological assay, described in the 30 August issue of Science , may be quicker than other methods, reducing the time it takes to detect a biological agent.
The assay consists of a chip covered with DNA strands. These strands will bind to a fragment of the genetic material of a biological agent, such as anthrax. The innovation is the way it spots that nefarious DNA quickly and accurately: After the chip has been exposed to a sample, the designers--Chad Mirkin, a chemist at Northwestern University in Evanston, Illinois, and his colleagues--simply apply a solution containing gold nanoparticles. These particles are covered with DNA strands that grab a different part of the agent's DNA. That means the gold particles will anchor themselves to the chip only if they encounter the agent's DNA.
The anchored particles will shine when scanned with a laser, because Mirkin's team doped the particles with a dye that scatters laser light. That trick makes the assay highly versatile. Because different dyes scatter different colors, the researchers can test for several targets at a time by color-coding the targets to make anthrax, say, blue and Ebola green. Mirkin says the chip is hundreds of times more sensitive than existing tests.
"It's a very exciting technique," says chemist Mark Wightman of the University of North Carolina, Chapel Hill. "It's a really neat and simple way to ID specific DNA and RNA fragments--and it doesn't seem to be pie in the sky." Potential applications include use as a bioweapons sensor or diagnostic test that can be performed at a clinic rather than being sent to a lab.
Chad Mirkin's home page