Temperature-Responsive Hydrogel-Coated Gold Nanoshells.

Gold nanoshells (~160 nm in diameter) were encapsulated within a shell of temperature-responsive poly(-isopropylacrylamide--acrylic acid) (P(NIPAM--AA)) using a surface-bound rationally-designed free radical initiator in water for the development of a photothermally-induced drug-delivery system. The morphologies of the resultant hydrogel-coated nanoshells were analyzed by scanning electron microscopy (SEM), while the temperature-responsive behavior of the nanoparticles was characterized by dynamic light scattering (DLS). The diameter of the P(NIPAM--AA) encapsulated nanoshells decreased as the solution temperature was increased, indicating a collapse of the hydrogel layer with increasing temperatures.

Thermal stability of mono-, bis-, and tris-chelating alkanethiol films assembled on gold nanoparticles and evaporated "flat" gold.

The thermal stability of SAMs generated from the adsorption of n-octadecanethiol (n-C18), 2-hexadecylpropane-1,3-dithiol (C18C2), 2-hexadecyl-2-methylpropane-1,3-dithiol (C18C3), and 1,1,1-tris(mercaptomethyl)heptadecane (t-C18) on colloidal gold and evaporated "flat" gold was investigated. The optical extinction of the monolayer-protected nanoparticles (MPCs) was monitored as a function of thermal stress by using ultraviolet-visible (UV-vis) spectroscopy, which revealed that the evolution of the surface plasmon resonance varied with the nature of the adsorbate. Specifically, MPCs functionalized with monodentate n-C18 showed the fastest red shift of the surface plasmon resonance while those functionalized with tridentate t-C18 showed the slowest red shift, with those derived from the bidentates C18C2 and C18C3 falling in between, suggesting a correlation between film stability and the degree of chelation.

SAMs on gold derived from the direct adsorption of alkanethioacetates are inferior to those derived from the direct adsorption of alkanethiols.

Self-assembled monolayers (SAMs) on gold derived from the direct adsorption of thioacetic acid S-decyl ester (C10SAc) and thioacetic acid S-octadecyl ester (C18SAc) were compared to the corresponding SAMs derived from the analogous adsorption n-decanethiol (C10SH) and n-octadecanethiol (C18SH). All SAMs were characterized using ellipsometry, contact angle goniometry, polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and X-ray photoelectron spectroscopy (XPS). The comparison revealed that the SAMs generated from the thioacetates are not as densely packed and well ordered as the SAMs generated from the thiols.

Preparation, characterization, and chemical stability of gold nanoparticles coated with mono-, bis-, and tris-chelating alkanethiols.

A systematically varying series of monolayer-protected clusters (MPCs) was prepared by exposing small gold nanoparticles ( approximately 2 nm in diameter) to the following four adsorbates: n-octadecanethiol ( n - C18), 2-hexadecylpropane-1,3-dithiol ( C18C2), 2-hexadecyl-2-methylpropane-1,3-dithiol ( C18C3), and 1,1,1-tris(mercaptomethyl)heptadecane ( t - C18). The resultant MPCs were characterized by solubility studies, UV-vis spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FT-IR). All of the MPCs were soluble in common organic solvents; moreover, analysis by TEM showed that the core dimensions were unaffected by exposure to any of the adsorbates.

Rationally designed ligands that inhibit the aggregation of large gold nanoparticles in solution.

Hexadecanethiol (n-C16), 2,2-dimethylhexadecane-1-thiol (DMC16), and the multidentate thiol-based ligands 2-tetradecylpropane-1,3-dithiol (C16C2), 2-methyl-2-tetradecylpropane-1,3-dithiol (C16C3), and 1,1,1-tris(mercaptomethyl)pentadecane (t-C16) were evaluated for their ability to stabilize large gold nanoparticles (>15 nm) in organic solution. Citrate-stabilized gold nanoparticles (20-50 nm) treated with the ligands were extracted from aqueous solution and dispersed into toluene. The degree of aggregation of the gold nanoparticles was monitored visually and further confirmed by UV-vis spectroscopy and dynamic light scattering (DLS).