A common type of lab test used in research and medicine can be made three million times more sensitive, raising hopes that certain cancers and Alzheimer's disease can be detected earlier.

That is the conclusion of new research by Princeton University engineers, published in the journal Analytical Chemistry, which describes an improved lab test that uses nanotechnology.

The test is called a fluorescent immunoassay, a laboratory staple for decades. It relies on antibodies that bind with specific proteins or biomarkers in a sample of fluid, such as blood or urine. The antibodies are "labeled" in such a way that they emit a fluorescent glow — indicating that the target protein is present.

The Princeton researchers used an array of nano-antennas to amplify this type of fluorescence so that targeted proteins, such as those that may herald the presence of certain cancers, could be detected at much lower levels.

The antenna arrays consist of glass pillars measuring just 60 billionths of a meter in height, each capped with a tiny gold disk. The pillars also have smaller gold dots on their sides.

The system acts somewhat like the wooden body of a violin, which transmits the vibrations of the strings to the surrounding air, said senior author Stephen Y. Chou, a professor of electrical engineering at Princeton. "Without the body, you'd struggle to hear the sound," he said.

Chou and his colleagues evaluated their technology on fluid containing a standard lab protein called human immunoglobin G — ordinarily detectable at a concentration of about one-billionth of a mole (a basic unit in chemistry) per liter. The team detected the protein at a concentration three million times lower.

The test could help diagnose Alzheimer's disease, which researchers try to detect by taking samples of cerebrospinal fluid, a relatively invasive procedure. Chou's technology, which detects much smaller concentrations in blood, "would be much easier and faster to use," said Yueming Li, a researcher at Memorial Sloan-Kettering Cancer Center who advised Chou on the research.

The group is conducting further research to detect biomarkers for specific diseases, such as breast and prostate cancers.

— Tom Avril