SERS performance of gold nanotubes obtained by sputtering onto polycarbonate track-etched membranes.

Surface-enhanced Raman scattering (SERS) is a powerful and versatile tool for studying molecules on metallic surfaces with great impact on areas such as electrochemistry, catalysis and related subjects. The search for new SERS-active substrates with high performance, namely high enhancement factors and reproducibility, is currently the main focus of several research groups. Here is shown an alternative easy and inexpensive synthetic approach to a SERS-substrate comprised of gold nanotubes obtained by the sputtering onto polycarbonate track-etched membranes used as template. Its SERS performance was evaluated by mapping (10 × 10) µm(2) areas and resulted in average enhancement factors that span from 2.3 × 10(3) to 1.2 × 10(5) with a maximum enhancement factor of 2.5 × 10(5). The enhancement depended strongly on the template pore diameter, with the best performance obtained when membranes with pore diameters of 400 nm were used as template. Further analysis showed that the larger enhancements came from coalesced gold nanotubes and detection of the dye rhodamine 6G at concentrations as low as 0.1 nM was possible. These results put this substrate as a valuable and easy-to-fabricate tool for studying and detecting molecules on surfaces. The proposed methodology could be easily adapted to other metals, such as silver and copper.

High performance gold nanorods and silver nanocubes in surface-enhanced Raman spectroscopy of pesticides.

The behavior of Au nanorods and Ag nanocubes as analytical sensors was evaluated for three different classes of herbicides. The use of such anisotropic nanoparticles in surface-enhanced Raman scattering (SERS) experiments allows the one to obtain the spectrum of crystal violet dye in the single molecule regime, as well as the pesticides dichlorophenoxyacetic acid (2,4-D), trichlorfon and ametryn. Such metallic substrates show high SERS performance at low analyte concentrations making them adequate for use as analytical sensors. Density functional theory (DFT) calculations of the geometries and vibrational wavenumbers of the adsorbates in the presence of silver or gold atoms were used to elucidate the nature of adsorbate-nanostructure bonding in each case and support the enhancement patterns observed in each SERS spectrum.

Investigations of different carbohydrate anomers in copper(II) complexes with D-glucose, D-fructose, and D-galactose by Raman and EPR spectroscopy.

With the aim of verifying different carbohydrate anomers coordinated to copper(II) ions, some copper(II) complexes with D-glucose (Glc), D-fructose (Fru), and D-galactose (Gal) were prepared and investigated by spectroscopic techniques. Their compositions were verified by elemental, ICP-AES and thermal analyses, in addition to conductivity measurements. The compounds isolated were consistent with the formula Na2[Cu2(carbohydrate)3].8H2O and Na[Cu2(carbohydrate)3].6H2O for the aldoses Glc and Gal, respectively, and Na2[Cu3(carbohydrate)4].8H2O in the case of the ketose, Fru. EPR spectra of these solids showed a rhombic environment around the metal center and suggested the presence of different anomers of the carbohydrates in each case. By Raman spectroscopy, it was possible to verify the predominance of the beta anomer of d-glucose in the corresponding copper complex, while in the free ligand the alpha anomer is predominant. In the case of the analogous complex with d-galactose, the spectrum of the complex shows bands of both anomers (alpha and beta) in approximately the same relative intensities as those observed in the isolated free ligand spectrum. On the other hand, for the complex with d-fructose a mixture of both furanose (five-membered ring) and pyranose (six-membered ring) structures was detected with prevalence of the furanose structure. Based on variations in the relative intensities of characteristic Raman bands, the binding site for copper in the fructose ligand was identified as most likely the 1-CH2OH and the anomeric 1-OH, while in beta-D-glucose it is presumably the anomeric 1-OH and the O-5 atom. These results indicated that EPR and Raman spectroscopy are suitable supporting techniques for the characterization of carbohydrate anomers coordinated to paramagnetic ions.