Ultrahighly Sensitive Surface-Enhanced Raman Spectroscopy Film of Silver Nanoparticles Dispersed in Three Dimensions on a Thin Alumina Nanowire Framework

To develop highly sensitive surface-enhanced Raman spectroscopy (SERS) films, various types of aggregated Ag nanowire (NW) and nanoparticle (NP) complex structures were fabricated using anodic aluminum oxide (AAO) templates and thermal evaporation. Aggregated AgNW structures with numerous tapered nanogaps were fabricated via Ag deposition on aggregated thin alumina nanowires of different lengths. AgNP complex structures were obtained by collapsing vertically aligned thin alumina nanowires 1 μm in length and depositing AgNPs on their tops and sides using surface tension during ethanol drying after functionalization. The Raman signal enhancement factors (EFs) of the samples were evaluated by comparing the SERS signal of the thiophenol (TP) self-assembled monolayer (SAM) on the nanostructures with the Raman signal of neat TP. EFs as high as ~2.3 × 107 were obtained for the optimized aggregated AgNW structure (NW length of 1 μm) and ~3.5 × 107 for the optimized AgNP complex structure. The large EF of the AgNP complex film is attributed mainly to the AgNPs dispersed in three dimensions on the sides of the thin alumina nanowires, strongly implying some important, relevant physics yet to be discovered and also a very promising nanostructure scheme for developing ultrahighly sensitive SERS films with EF > 108.

Enhanced solid-state plasmon catalyzed oxidation and SERS signal in the presence of transition metal cations at the surface of gold nanostructures

The effect of several metal cations (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) on the photochemical conversion of 4-aminothiophenol (4-ATP) into 4,4'-dimercaptoazobenzene (DMAB) is probed using surface enhanced Raman scattering (SERS). The coupling reaction is carried out on the surface of Au nanoparticles and Au nanorods using 532 nm and 632.8 nm laser excitations, respectively, in the absence and presence of metal cations. Here, we report that DMAB formation on the surface of Au nanostructures - when carried out in the solid state - is augmented significantly (by a factor of 1.98 to 4.07 and 3.34 to 5.74 for Au nanoparticle and Au nanorod substrates, respectively, and depending on the metal). Furthermore, the SERS signal is also markedly enhanced. Thus, the results underpin a new way of carrying out a photochemical reaction with a higher yield along with a higher SERS signal.

The unusual visible photothermal response of free standing multilayered films based on plasmonic bimetallic nanocages

An unusual photothermal response in the visible region has been observed in free standing multilayered films based on the plasmonic bimetallic Au and Ag nanocages (Ag@AuNCs).