Engineers have shown that nanosized silver cubes can make diagnostic tests that rely on fluorescence easier to read by making them more than 150 times brighter. Combined with an emerging point-of-care diagnostic platform already shown to be able to detect small traces of viruses and other biomarkers, the approach could allow such tests to become much cheaper and more widespread.
The results appeared online on May 6 in the journal Nano Letters.
Plasmonics is a scientific field that traps energy in a feedback loop called a plasmon onto the surface of silver nanocubes. When fluorescent molecules are sandwiched between one of these nanocubes and a metal surface, the interaction between their electromagnetic fields causes the molecules to emit light much more vigorously. Maiken Mikkelsen, the James N. and Elizabeth H. Barton Associate Professor of Electrical and Computer Engineering at Duke, has been working with her laboratory at Duke to create new types of hyperspectral cameras and superfast optical signals using plasmonics for nearly a decade.
At the same time, researchers in the laboratory of Ashutosh Chilkoti, the Alan L. Kaganov Distinguished Professor of Biomedical Engineering, have been working on a self-contained, point-of-care diagnostic test that can pick out trace amounts of specific biomarkers from biomedical fluids such as blood. But because the tests rely on fluorescent markers to indicate the presence of the biomarkers, seeing the faint light of a barely positive test requires expensive and bulky equipment.
«Our research has already shown that plasmonics can enhance the brightness of fluorescent molecules tens of thousands of times over,» said Mikkelsen. «Using it to enhance diagnostic assays that are limited by their fluorescence was clearly a very exciting idea.»
«There are not a lot of examples of people using plasmon-enhanced fluorescence for point-of-care diagnostics, and the few that exist have not been yet implemented into clinical practice,» added Daria Semeniak, a graduate student in Chilkoti’s laboratory. «It’s taken us a couple of years, but we think we’ve developed a system that can work.»
In the new paper, researchers from the Chilkoti lab build their super-sensitive diagnostic platform called the D4 Assay onto a thin film of gold, the preferred yin to the plasmonic silver nanocube’s yang. The platform starts with a thin layer of polymer brush coating, which stops anything from sticking to the gold surface that the researchers don’t want to stick there. The researchers then use an ink-jet printer to attach two groups of molecules tailored to latch on to the biomarker that the test is trying to detect. One set is attached permanently to the gold surface and catches one part of the biomarker. The other is washed off of the surface once the test begins, attaches itself to another piece of the biomarker, and flashes light to indicate it’s found its target.
Story Source: Materials provided by Duke University. Original written by Ken Kingery. Note: Content may be edited for style and length.