In this chapter, we revise some of the most relevant and widely used synthetic routes available for the preparation of metallic silver nanoparticles. Particular emphasis has been focused in the rationale involved in the formation of the nanostructures, from the early metallic silver atoms formation, passing by atoms nucleation and concluding in the growth of silver nanostructures. We hope the reader will find in this chapter a valuable tool to better understand the relevance of the experimental conditions in the resulting silver nanoparticle size, shape and overall properties.
In this work, we report a simple strategy to obtain ultrasensitive SERS nanostructures by self-assembly of Au nanospheres (NSs). This novel protocol allow us to obtain in a reproducible manner Au NS dimers using cucurbit[6]uril (CB[6]) molecules as linkers. The resulting dimers are stable in colloidal dispersion over several days, generating in this way nanostructures with highly reproducible hot spots. This feature is due to the precise subnanometric control of the molecules that generates interparticle distance and, at the same time, of the capability of placing analyte molecules just within these junctions of ultrahigh field enhancement due to the host−guest properties of the CB[6] molecule. The dimer formation is based on the modification of the metal surface with cysteamine molecules (Cys) previous incubation with CB [6] molecules. The cysteamine-functionalized NSs (Cys/ NSs) are positive charged due to the protonation of the amine groups of the Cys molecule at the working pH. These positive groups interact through H-bonds with the carbonyls groups at the portal of the CB[6] molecules. The dimer formation is based on the stoichiometric control between Cys/NPs and CB[6] (ratio 2:1), generating a gap of 1.8 nm and giving rise to SERS enhancements of around 10 8 . The host−guest properties of the CB [6] molecule are used to detect the average SERS enhancement produced by adding methyl viologen (MV) as plasmonic probe. It was found that the average analytical enhancement factor (AEF) for MV is as good as that obtained for the CB[6] itself (around 10 8 ).
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