The nanoparticle probes consist of 13 nm-diameter gold particles attached to oligonucleotide and Raman-active dye molecules. The oligonucleotide molecules bind to specific target DNA, while the dye molecule acts as the fingerprint. The scientists can select the dye molecule according to the target that the probe is designed to reveal.

"By providing a near infinite number of signals, this advance allows researchers to quickly and accurately screen a sample for an extraordinarily large number of diseases simultaneously," said Chad Mirkin, director of Northwestern's Institute for Nanotechnology.

The Northwestern technique employs the nanoparticle probes in combination with a chip spotted with strands of DNA that recognize different disease targets. If the disease target is present in the sample under test, it binds to the appropriate spot on the chip. The corresponding nanoparticle probes also latch onto the disease target at that spot.

Then the scientists wash the chip and treat it with photographic developing solution, coating the gold nanoparticles with silver. Examining the treated chip with a Raman spectrometer reveals which particular dye molecules, and hence which disease targets, are present.

"The silver enhances the signal by many orders of magnitude, creating a highly sensitive method for detecting DNA," added Mirkin. "Our technique seems to surpass conventional fluorescence-based methods in almost every category - sensitivity, selectivity, ease of use and speed - and has the potential to be very inexpensive."

Mirkin and his team used their technique to detect genetic markers for six biological agents, including hepatitis A, smallpox and HIV. They reported their work in Science.