1, Northeastern Univ, Boston, Massachusetts, United States
Since Fleischmann first discovered the phenomenon of enhanced Raman signals from adsorbed pyridine on roughened Ag surfaces in 1974, surface-enhanced Raman scattering (SERS) has been used as an ultrasensitive vibrational spectroscopic technique to detect molecules on or near the surface of plasmonic nanostructures, greatly extending the role of standard Raman spectroscopy. More recently, this technique has been used to design novel nanoprobes or “SERS tags” that combine metallic nanostructures and specific organic Raman reporter molecules. In this paper, we report the fabrication, optical properties and SERS efficiency of a new family of SERS tags comprised of silica nanoparticles ca. 150 nm in diameter with an Au0.5Ag0.5 alloy shell ca. 25 nm in thickness.
Raman reporter dye molecules were chemically and/or physically adsorbed onto the surface of the SiO2@Au0.5Ag0.5 nanoparticles which were then coated with a Ag layer. Compared to the monometallic Au and Ag nanoshells with same diameter core and shell thickness, the Au/Ag alloys show an excellent enhancement in Raman intensities. Binding studies with polymer microspheres are also described as a demonstration of the potential of these bright dye-labeled SERRS-encoded tags for high-throughput screening flows. These microspheres are commonly used as standards and controls in flow cytometry measurements, as well as solid supports for multiplexed molecular measurements. The combination of SERS tags with flow cytometry for analyzing blood and other cell types in clinical samples provides improved multiplexing capability, offering a significant advantage over conventional flow cytometry methods. The bimetallic SERS tags, which present a stronger enhancement in Raman intensities compared to the monometallic tags can be potentially used for multiplex characterization of small molecule metabolites in biological systems