Gold-coated silica

In their experiments the authors worked with gold-coated silica spheres, with self-assembled monolayers of mixtures of undecanethiols and co-hydroxy undecane thiols, to vaiy the contact angle between 20 and 100°. The results were compared with sessile drop measurements on the same system. A systematic difference up to 20° for the receding angles) between the two sets of results was observed, but since these differences depend on the nature of the solid surface it was not possible to pinpoint the origin definitely. A remarkable feature was that in the AFM method, hysteresis was very small, if not absent. Anyhow, this appears to be a promising technique. 

In Fig. 4, the plasmon resonance for gold coated silica is plotted as a function of the shell thickness (for fixed core thickness of 10 nm). In Fig. 6 we see the effects of changing either the core or medium refractive index. 

Schematic diagrams for the synthetic schemes are illustrated in Fig. 15.5. To briefly summarize, silica nanoparticles were synthesized by the Stober-method and then coated with a Sn layer, which acts as a linker site for gold deposition. Gold layers were coated on the Sn-functionaUzed silica nanoparticles by reduction of HAuCLt. Finally, the gold-coated silica nanoparticles were covered...

Schematic diagram for the synthesis of gold-coated silica nanoparticles. 

Experimental scheme for preparation of PPV nanocomposites doped with gold-coated silica nanoparticles. Reprinted with permission from Y.T. Limefa/., Synth. Mat 128,133 (2002). Copyright 2002 Elsevier. 

A detailed study by Grieser and co-workers [169] of the forces between a gold-coated colloidal silica sphere and a gold surface reveals the preferential adsorption of citrate ions over chloride to alter the electrostatic interaction. 

Kriger, M. S., Cook, K. D., and Ramsey, R. S. (1995). Durable gold-coated fused silica capillaries for use in electrospray mass spectrometry. Anal. Chem. 67, 385—389. 

Vanhoutte et al. [81] compared various nano-ESI tips. With the uncoated non-tapered 20-pm-lD fused-silica tips, delivered with the Mcromass NanoFlow probe, the sensitivity was dependent of the mobile-phase compositiom Replacing these tips by uncoated tapered ones (20 9 pm ID) showed some improvement, while the best results, especially at low percentages of methanol in the mobile phase, were achieved with gold-coated tapered fused-silica tips. 

Instruments IR-85 Fourier Transform infrared spectrometer, through an IBM GC-IR interface. The interface consisted of a gold-coated Pyrex light-pipe with potassium bromide windows. A scan rate of 6 scans/sec and a spectral resolution of 8 cm- - were used for data acquisition. Samples were introduced into the system via splitless injections. A fused silica capillary column, 30 m x 0.32 mm i d DB-WAX (dj 1.0 pm), was employed with the outlet end connected directly to the GC-IR light-pipe entrance. Helium was used as the carrier gas at an average linear velocity of 41.4 cm/sec (35°C). No make-up gas was employed in the system. The column temperature was programmed from 35°C to 180°C at 2°C/min. The GC-IR light-pipe assembly was maintained at 170°C. 

Testing procedure In general, standard methods were used, with some improvements to obtain better resolution. A photoacoustic detector was used to obtain spectra of fumed silica. A carbon black background was used. In studies of adhesion of coatings on metal substrates, a gold coated background was used as the reference. 4 Diffuse respectra, and kaolin. 2 A... 

Kriger, M.S. Cook, K.D. Ramsey, R.S. Durable Gold-Coated Fused Silica Capillaries for Use in Electrospray Mass Spectrometry, Anal. Chem. 67, 385-389 (1995). 

Experimentally, Thomas and coworkers found that hydrocarbon-coated gold nanoparticles, with a diameter of 3.5 nm, segregated to the interface between the microdomains of poly(styrene-btock-ethylene propylene) (PS-fe-PEP) copolymer, whereas larger hydrocarbon-coated silica nanoparticles (21.5nm in diameter) were located at the center of the PEP domains [79], In the absence of specific enthalpic interactions between the two types of nanoparticles and the polymer matrix, the result suggests a profound influence of entropic contributions to the self-organization process. For large particles, the decrease in conformational entropy of the respective polymer subchains after particle sequestration is dominant, whereas for smaller particles, the decrease in entropy is outweighed by the particle translational entropy. 

V. Salgueirino-Maceira, M. A. Corsea-Duarte, M. Earle, A. Lopez-Quintela, K. Sieradzki and R. Diaz, Bifunctional gold-coated magnetic silica spheres. Chem. Mater., 18,2701-2706 (2006). 

Another instrumental development is based on the fact that the generation of smaller droplets is more favorable in terms of droplet evaporation during ESI, of sensitivity and the abihty to preserve non-covalent molecular associates. Thus, nanoelectrospray ionization (nESI) has been developed [68], where the analyte is sprayed from a gold-coated fused-silica capillary with a tip diameter of 1-5 pm rather than from capillaries with a 100-150-pm tips that are used in conventional (pneumatically assisted) ESI. In nESI, flow-rates as low as 20 nl/min can be nebulized. Thus, gentler operating conditions (temperature, gas flows, needle voltage) can be achieved. In order to more readily implement nESI in LC-MS operation, integrated chip-based nano-LC-nESI devices have also been developed [69]. 

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