Device eliminates wait for DNA results

Science News, March 27, 1999 by C. Wu

Crime investigators want forensic tests to be fast and accurate. Unfortunately, such tests are often slow and prone to error. Whenever a person intervenes in the procedure, opportunities for mistakes increase.

Now, researchers have designed a machine that performs a standard DNA test on blood samples from start to finish--without human intervention. Nanyan Zhang, Hongdong Tan, and Edward S. Yeung at the Department of Energy's Ames (Iowa) Laboratory and Iowa State University in Ames describe their prototypical device in the March 15 Analytical Chemistry. It can work on blood samples as small as 1 microliter.

Traditional DNA analysis can match bloodstains found at a crime scene, but getting results from a lab usually takes 4 to 6 weeks. The new system "would give you enough information to rule in or rule out certain people in about 2 1/2 hours," says Yeung.

Existing technology also permits automation of certain steps of the process, says Yeung, but a person still must transfer samples between the steps. That increases the chance of contamination and other mishaps.

The prototype carries out a sequence of several operations automatically on tiny blood samples. Each sample travels through a long, thin capillary tube. In the first section, a brew of chemicals breaks open the blood cells. The chemicals amplify the minuscule amount of DNA to a measurable quantity via a process called the polymerase chain reaction, or PCR (SN: 10/23/93, p. 262).

The second section of the tube separates the amplified DNA fragments. The pieces of DNA are then identified by beaming a laser at them and detecting their fluorescence.

In order to use PCR on whole blood, rather than on isolated DNA, Yeung and his coworkers had to modify the standard procedure.

"Blood is one of the worst materials because it contains a lot of proteins, and proteins affect the enzymatic reactions in PCR," he explains. The Ames group, therefore, chose enzymes that work in the presence of various blood proteins.

The researchers' prototype analyzes and compares 8 DNA samples simultaneously, although it could easily handle 100 without major changes in design, Yeung says.

Many companies are developing miniature chemistry labs on microchips so that forensic-and environmental-test devices can be portable (SN: 8/15/98, p. 104). Unlike these other miniaturized instruments, the Iowa system "does a lot of samples in parallel. That's what's unique about it," says Steven A. Soper of Louisiana State University in Baton Rouge. In a clinical setting, the Iowa device could screen many blood samples for disease-causing genes, reducing delays and cost, adds Soper.

Though not as small as a lab-on-a-chip, the Ames group's prototype could fit in the back of a van, says Yeung. Taken to a crime scene, the machine could examine evidence on the spot.