A major goal in immunoassay research is to improve the sensitivity of detection. Achieving this goal could enable early detection and treatment of diseases such as cancer and Alzheimer's by allowing doctors to recognize telltale markers in much lower concentrations than was previously practical.
Princeton University researchers have applied glass and gold nanostructures to address this issue, and have succeeded in increasing the fluorescence signal—and the detection limit—three million times.1 This means that to produce a measurable glow, three million times fewer biomarkers need to be present compared to a conventional immunoassay. The development opens new opportunities for early disease detection and treatment—and perhaps equally important, it requires no changes for researchers and technicians: The new procedure involves exactly the same steps.
The breakthrough derives from use of an artificial material called D2PA, which researchers in the lab of Stephen Chou, Princeton's Joseph C. Elgin Professor of Engineering, have been developing for several years. D2PA is composed of a thin layer of gold nanostructures surrounded by glass pillars 60 nm in diameter and spaced 200 nm apart. Each pillar is capped with gold, and its sides are speckled with gold dots just 10 to 15 nm in diameter. Previous work has shown that this structure boosts the collection and transmission of light in unusual ways—increasing Raman scattering a billion-fold. The current work demonstrates an even greater signal enhancement with fluorescence.
In a typical immunoassay, a sample of fluid such as blood is added to glass vials containing antibodies that bind to biomarkers associated with disease. Another set of antibodies, labeled with a fluorescent molecule, are then added as well. If the suspected biomarkers are not present in the patient's fluid sample, the fluorescent antibodies do not attach and are washed away—so no glow is evident. The new technology allows fluorescence to be seen when just a few antibodies find their mark.
In addition to diagnostics, immunoassays are commonly used in drug discovery and other biological research. Chou is now conducting tests of the D2PA-enhanced immunoassay for detecting breast and prostate cancers, and is collaborating with researchers at Memorial Sloan-Kettering Cancer Center (New York, NY) to develop tests to detect Alzheimer's disease very early.
1. L. Zhou et al., Anal. Chem., 84, 10, 4489 (2012).