Future Blood Tests May Use Tiny Bar-codes To Speed Disease Diagnosis

Details about the analytical test, which appears promising in experimental studies, are scheduled to appear in the May 19 print issue of the Journal of the American Chemical Society, a peer-reviewed publication of the American Chemical Society, the world's largest scientific society. The study was published online today (April 27) on the journal's Web site.

"This test has the potential to completely revolutionize medical diagnostics," says Chad A. Mirkin, Ph.D., head of the study and director of Northwestern's Institute for Nanotechnology, located in Evanston, Ill. He says that the test will bring efficient, high-tech DNA diagnostics to unprecedented settings, including the battlefield and Third World villages, as well as hospitals and the home.

The test is easier, faster, more accurate and less expensive than polymerase chain reaction (PCR), which is currently used to detect and quantify DNA samples, he says. The new test, called bio-bar-code amplification (BCA), could be ready for marketing in as little as one year, Mirkin says.

Unlike conventional tests that require one or more vials of blood, the new test allows a single drop of blood to paint a patient's comprehensive disease profile in about the same amount of time it takes for a routine doctor's visit.

The test is based on a set of chemical probes that are used to tag disease markers. If one is trying to detect exposure to anthrax, for instance, a set of probes is prepared that represents a unique molecular tag for anthrax-related DNA. One probe includes a magnetic nanoparticle containing a single DNA strand that matches the target (anthrax) DNA. The other probe consists of a gold nanoparticle attached to a DNA strand that also matches the target (anthrax) DNA. The gold nanoparticle is also attached to hundreds of DNA bar-code sequences that are unique identification tags for the anthrax target DNA. If anthrax is present in the blood, its DNA marker is then sandwiched between the two probes, separated magnetically, scanned and identified.

So far, the test has proven accurate in detecting anthrax lethal factor — a marker for anthrax exposure. It has also been used to detect prostate specific antigen — a marker for prostate cancer — at low levels. One could conceivably develop a bar-code for every disease-related protein or DNA sequence, according to Mirkin.

Current scanners that can read the bar-codes are bulky, stationary instruments, but a handheld prototype is in development. If all goes well in future studies, bar-code scanning of blood could be developed for home use, allowing consumers to make their own initial medical diagnoses quickly and easily, says Mirkin.

Nanosphere, a company that develops nanoparticle-based biodetection technology for medical diagnostics, was started four years ago by Mirkin.

Funding for this research was provided by the Air force Office of Scientific Research, the Defense Advanced Research Projects Agency, the National Science Foundation and the National Institutes of Health.