Improved stability of gold nanoparticles (AuNPs) in water is achieved by capping the particles. Such stability improvements are significant because of the potential applications of AuNPs in various biologically relevant areas. The highly stabilized water‐soluble AuNPs described in this study have precisely tunable sizes ranging from 2 to 5 nm (see figure; inset: fast Fourier transform) and a narrow monodispersity, and are prepared by using nucleotides as capping ligands.

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The Piers-Rubinsztajn reaction, involving B(C(6)F(5))(3)-catalyzed siloxane formation from hydrosilanes + alkoxysilanes, is tolerant of a wide variety of functional groups, and provides a generic strategy for the preparation of structurally complex functional silicones.

Differences in the wavelengths of the surface plasmon band of gold nanoparticles (AuNP)--before and after particle aggregation--are widely used in bioanalytical assays. However, the gold surfaces in such bioassays can suffer from exchange and desorption of noncovalently bound ligands and from nonspecific adsorption of biomolecules. Silica shells on the surfaces of the gold can extend the available surface chemistries for bioconjugation and potentially avoid these issues. Therefore, silica was grown on gold surfaces using either hydrolysis/condensation of tetraethyl orthosilicate 1 under basic conditions or diglyceroxysilane 2 at neutral pH. The former precursor permitted slow, controlled growth of shells from about 1.7 to 4.3 nm thickness. By contrast, 3-4 nm thick silica shells formed within an hour using diglyceroxysilane; thinner or thicker shells were not readily available. Within the range of shell thicknesses synthesized, the presence of a silica shell on the gold nanoparticle did not significantly affect the absorbance maximum (~5 nm) of unaggregated particles. However, the change in absorbance wavelength upon aggregation of the particles was highly dependent on the thickness of the shell. With silica shells coating the AuNP, there was a significant decrease in the absorbance maximum of the aggregated particles, from ~578 to ~536 nm, as the shell thicknesses increased from ~1.7 to ~4.3 nm, because of increased distance between adjacent gold cores. These studies provide guidance for the development of colorimetric assays using silica-coated AuNP.

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