Princeton researchers dramatically improved the sensitivity of immunoassays, a common medical test, using the nanomaterial shown here. The material consists of a series of glass pillars in a layer of gold. Each pillar is speckled on its sides with gold dots and capped with a gold disk. Each pillar is just 60 nanometers in diameter, 1/1,000th the width of a human hair. (Image courtesy of Stephen Chou)
A laboratory test used to detect disease and perform biological research could be made more than 3 million times more sensitive, according to Princeton University researchers who combined standard biological tools with a breakthrough in nanotechnology.
The increased performance could greatly improve the early detection of cancer, Alzheimer’s disease and other disorders by allowing doctors to detect far lower concentrations of telltale markers than was previously practical.
The breakthrough involves a common biological test called an immunoassay, which mimics the action of the immune system to detect the presence of biomarkers — the chemicals associated with diseases. When biomarkers are present in samples, such as those taken from humans, the immunoassay test produces a fluorescent glow that can be measured in a laboratory. The greater the glow, the more of the biomarker is present. However, if the amount of biomarker is too small, the fluorescent light is too faint to be detected. A major goal in immunoassay research is to improve this detection limit.
The Princeton researchers tackled this limitation by using nanotechnology to greatly amplify the faint fluorescence from a sample. By fashioning glass and gold structures so small they could only be seen with a powerful electron microscope, the scientists were able to drastically increase the fluorescence signal compared to conventional immunoassays, leading to a 3-million-fold improvement in the limit of detection. That is, to produce a measurable glow, the enhanced immunoassay would require 3 million times fewer biomarkers to be present compared to a conventional immunoassay.
"This advance opens many new and exciting opportunities for immunoassays and other detectors, as well as in disease early detection and treatment," said Stephen Chou , Princeton’s Joseph C. Elgin Professor of Engineering, who led the research team. "Furthermore, the new assay is very easy to use, since for the person conducting the test, there will be no difference from the old one — they do the procedure in exactly the same way."
The key to the breakthrough lies in a new artificial nanomaterial called D2PA, which has been under development in Chou’s lab for several years. D2PA is a thin layer of gold nanostructures surrounded by glass pillars just 60 nanometers in diameter. (A nanometer is one billionth of a meter; that means about 1,000 of the pillars laid side by side would be as wide as a human hair.) The pillars are spaced 200 nanometers apart and capped with a disk of gold on each pillar. The sides of each pillar are speckled with even tinier gold dots about 10 to 15 nanometers in diameter. In previous work, Chou has shown that this unique structure boosts the collection and transmission of light in unusual ways — in particular, a billion-fold increase in an effect called surface Raman scattering. The current work now demonstrates a giant signal enhancement with fluorescence.
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