Single Molecule Detection Surface-Enhanced Raman Scattering Substrates by Electroless Synthesis of Ag Nanoparticles on Nanostructured Silicon Films

Abstract

Surface-enhanced Raman scattering (SERS) substrates have been demonstrated through electroless reduction of silver on nanostructured Si films. At low analyte concentrations (10−9 - 10−10 M), the SERS signal shows temporal and sudden spectral fluctuations characteristic of single molecules (SM). When this intermittent SERS radiation is monitored with a CCD video- camera, blinking bright spots are observed attributable to SERS emission from SMs finding ultrahigh SERS gain sites. The laser, once focused on the SERS substrate, is found to induce Ostwald ripening and concomitant formation of aggregates, which are essential for SM detection. Unlike the previous single molecule SERS demonstrations, which have employed citrate-reduced nanoparticles, it is not necessary to incubate the Ag in analyte solution for hours. Instead, single molecule SERS signal is observed immediately after the spotting of the analyte. This is likely due to the absence of any chemical agents on the Ag nanoparticle surfaces allowing quick analyte adsorption.