Plasmonic Patch Boosts Fluorescence for Biosensing, Bioimaging

To strengthen weak signals in fluorescence-based detection and imaging techniques, researchers have developed an inexpensive plasmonic patch that can increase fluorescence intensity up to 100×.

The patch, about a centimeter square, is based on a flexible and conformal elastomeric film with embedded plasmonic nanostructures. Its use does not require any change in testing protocols. After the sample is prepared, the patch is transferred onto its surface, and the sample is scanned as usual.

“It’s a thin layer of elastic, transparent material with gold nanorods or other plasmonic nanostructures absorbed on the top," said researcher Jingyi Luan. "These nanostructures act as antennae: They concentrate light into a tiny volume around the molecules emitting fluorescence. The fluorescence is dramatic, making it easier to visualize. The patch can be imagined to be a magnifying glass for the light.”

A multidisciplinary team at Washington University in St. Louis and the Air Force Research Laboratory (AFRL) at Wright-Patterson Air Force Base has developed a high-tech fix that utilizes metal nanostructures to increase the fluorescence intensity by up to 100× in medical diagnostic tests. Courtesy of Washington University in St. Louis.

Researchers demonstrated the application of the technology, using it to enhance the bioanalytical parameters of fluoroimmunoassays implemented in a standard 96-microplate format and an antibody microarray. The plasmonic patch consistently resulted in a more than two orders of magnitude fluorescence intensity enhancement. The improvement in the bioanalytical parameters was found to be consistent across different assay formats, target biomarkers, and fluorophores.

Researchers developed the patch to provide a relatively simple solution to uniform fluorescence enhancement. Existing techniques for boosting fluorescence signals, such as enzyme-based amplification, require extra steps and in some cases specialized, expensive readout systems.

“Using fluorescence for biodetection is very convenient and easy," said professor Srikanth Singamaneni, "but the problem is it’s not that sensitive, and that’s why researchers don’t want to rely on it.”

Researchers said that the newly developed patch will cost only about 5 cents per application, and that it can be used for both research applications and diagnostics. It could be particularly useful in a microarray, where simultaneous detection of tens to hundreds of analytes are enabled in a single experiment.

“The plasmonic patch will enable the detection of low-abundance analytes in combination with conventional detection methodologies, which is the beauty of our approach,” said researcher Rajesh Naik.

“It's a last step, just like a Band-Aid,” Singamaneni said. “You apply it, and the dimness problem in these fluorescence-based detection methods is solved.”

The research was published in Light Science & Applications (doi:10.1038/s41377-018-0027-8).

A collaborative team, including researchers at the School of Engineering & Applied Science and the School of Medicine at Washington University in St. Louis, developed a plasmonic patch designed to boost brightness in certain diagnostic tests. Courtesy of Washington University in St. Louis.