Scatterings image

The nanostructured surface of the shrink-wrap coated with a 10-nm-thick layer of gold and 5 nm-, 15 nm-, and 25-nm-thick layers of nickel (a, b, c, respectively).

Researchers at the University of California, Irvine, U.S.A., have developed a technique that uses shrink-wrap film to detect biomarkers for infectious diseases like HIV/AIDS and tuberculosis. Michelle Khine and colleagues use a thin coating of gold and nickel on a thermoplastic layer to boost the signal of fluorescent biomarkers (antibodies the immune system generates in response to a pathogen) by a thousand times, which could reduce the cost of diagnostics enough to make it accessible in most areas of the world (Opt. Mater. Express 4, 753).

According to the authors, heating the metal-coated thermoplastic polymer causes it to wrinkle into multi-scale composite structures that amplify the signal of even a single antibody molecule.  The technique involves tagging these biomarkers with fluorescent probes, which allows their detection via metal-enhanced fluorescence in near-infrared (NIR) light.

“The enhanced intensity of the biomarker signals is due to the excitation of localized surface plasmons in the metal,” explains first author and graduate student Himanshu Sharma. When the NIR light hits the wrinkles, the electromagnetic field is amplified, producing hotspots of intense fluorescence signals from the biomarkers. In one case, the team observed that signals from a single molecule of goat anti-mouse immunoglobulin (called IgG) antibody was enhanced by three orders of magnitude over that detected using a glass coverslip with two-photon excitation.

Although the researchers caution that much work is needed to further develop the technique, they expect their results to help in the creation of an integrated, low-cost detection device to trap and identify biomarkers.