3D Silver Dendrites for Single-molecule Imaging by Surface-enhanced Raman Spectroscopy

Discovery of surface-enhanced Raman scattering (SERS) followed by evolution of optical systems and nanoengineering approaches has paved a path to detection of essential organic molecules on solid SERS-active substrates from solutions at concentrations attributed to single-molecule ones, i. e. below 10(-15) M. However, in practical terms confident SERS-imaging of single molecules is still quite a challenge. In present work, we fabricated and comprehensively characterized tightly-packed 3D silver dendrites with prevalent chevron morphology that demonstrated ultrahigh sensitivity as SERS-active substrates resulted in 10(-18) M detection limit. Using these substrates we achieved SERS-imaging of single 5-thio-2-nitrobenzoic acid (TNB) molecule released from the attomolar-concentrated solution of of 5,5 '-dithio-bis-[2-nitrobenzoic acid] (DTNB), which is vital compound for chemical and biomedical analysis. In contrast to generally accepted belief about adsorption of only uniform monomolecular TNB layer on surface of silver nanostructures, we showed formation of a coating constituted by TNB layer and DTNB nanoclusters on the dendrites' surface at 10(-6)-10(-12) M DTNB concentrations confirmed by presence/absence of disulfide bonds signature in the SERS-spectra and by scanning electron microscopy. DTNB concentrations below 10(-14) M resulted in adsorption of TNB molecules in separated spots on the surface of silver nanostructures.