On the use of Au@Ag core-shell nanorods for SERS detection of Thiram diluted solutions.

Rod-shaped gold-silver core-shells (AuNR@Ag) were synthesized for an analysis of the amplification of Raman scattering (surface-enhanced Raman scattering, SERS). The microscopy characterization confirmed a hierarchically structured nanoparticle with well-defined size and morphology, however, with a degree of dispersion in terms of shell thickness and symmetry of Ag deposition. In this paper, we analyze the possible effects of such structural dispersion in the SERS spectra of 4-aminobenzothiol (4-ABT) and in its detection at low concentrations in solutions. The interpretation of experimental results was supported by classical electrodynamics simulations based on the boundary element method (BEM). We verified that even in the case of asymmetrical Ag deposition onto AuNRs, a large SERS normal may be observed, which leads to the possibility of using such nanostructures for SERS applications aiming at low analyte concentrations detections. We show that the SERS substrates based on such AuNR@Ag present very high sensitivity for the detection of ultra-low concentrations of 4-ABT reaching a detection limit of 1.10-15 mol L-1, which indicates the possibility of analytical applications in the detection of analytes such as pesticides.

Selective synthesis of silver nanoparticles onto potassium hexaniobate: structural organisation with bactericidal properties.

Silver-based nanocomposites are known to act as biocides against a series of microorganisms and are largely studied as an alternative to substitute conventional antibiotics that show decreasing efficacy. In this work, an eco-friendly method to synthesize silver nanoparticles assembled on the surface of hexaniobate crystals is reported. By means of ion exchange, K(+) ions of layered potassium hexaniobate were partially substituted by Ag(+) ions and the resulting material was exposed to UV light. The irradiation allowed the reduction of silver ions with consequent formation of silver nanoparticles located only on the hexaniobate surface, whereas Ag(+) ions located in the interlayer space remained in the ionic form. Increasing UV-light exposure times allowed controlling of the silver nanoparticle size. The antibacterial effects of the pristine potassium hexaniobate and of silver-containing hexaniobate samples were tested against Escherichia coli (E. coli). The antibacterial efficacy was determined to be related to the presence of silver in hexaniobate. An increasing activity against E. coli was observed with the decrease in silver nanoparticles size, suggesting that silver nanoparticles of distinct sizes interact differently with bacterial cell walls.