Interaction of alkanethiols with nanoporous cluster-assembled Au films

Photoacoustic Sensing of Trapped Fluids in Nanoporous Thin Films: Device Engineering and Sensing Scheme

Accessing fluid infiltration in nanogranular coatings is an outstanding challenge, of relevance for applications ranging from nanomedicine to catalysis. A sensing platform, allowing quantifying the amount of fluid infiltrated in a nanogranular ultrathin coating, with thickness in the 10-40 nm range, is here proposed and theoretically investigated by multiscale modeling. The scheme relies on impulsive photoacoustic excitation of hypersonic mechanical breathing modes in engineered gas-phase-synthesized nanogranular metallic ultrathin films and time-resolved acousto-optical read-out of the breathing modes frequency shift upon liquid infiltration. A superior sensitivity, exceeding 26 × 10³ cm²/g, is predicted upon equivalent areal mass loading of a few ng/mm². The capability of the present scheme to discriminate among different infiltration patterns is discussed. The platform is an ideal tool to investigate nanofluidics in granular materials and naturally serves as a distributed nanogetter coating, integrating fluid sensing capabilities. The proposed scheme is readily extendable to other nanoscale and mesoscale porous materials.

Interaction of L-cysteine with naked gold nanoparticles supported on HOPG: a high resolution XPS investigation

We report the results of a synchrotron-based high-resolution XPS study of the interaction of L-cysteine (Cys) with well-characterized colloidal gold nanoparticles (NPs, typical size 3-4 nm), which were pre-deposited on highly oriented pyrolytic graphite and then brought into contact with the aqueous solution of Cys by drop-casting. By comparison with data previously obtained for Cys deposition on flat Au substrates (single crystals and high quality films), we demonstrate the formation of a strong Cys/NP thiolate bond. The analysis of the line shape and adsorbate-induced Au 4f core level shift, backed by simulations of the NP structure, reveals the interaction of Cys with low-coordinated Au atoms belonging to the NP edge and corners. The analysis of the N 1s core-level indicates that neutral molecules are the most abundant species. The small facet size limits the formation of extended networks of zwitterionic molecules, typical of single crystal surfaces. This study provides a spectroscopic insight into the intense poisoning effect caused by a limited amount of Cys on Au catalysts described in previous reports.

Effect of coverage and defects on the adsorption of propanethiol on Au(111) surface: a theoretical study

Periodic density functional calculations have been carried out to investigate both the thiol adsorption on Au(111) surface and the reaction mechanism for the formation of the self-assembled monolayers, taking propanethiol as a representative example. The effect of coverage and surface defects (adatoms and vacancies) has been analyzed. It is found that the most stable physisorption (undissociated) site is an adatom site, whereas the chemisorption site for the thiol is a vacancy site or protrusion consisting of a pair of adatoms, followed by one adatom site. The results point out that the thiolate self-assembled monolayer adsorption process occurs preferentially on step edges.

Optical properties of Yeast Cytochrome c monolayer on gold: an in situ spectroscopic ellipsometry investigation

The adsorption of Yeast Cytochrome c (YCC) on well defined, flat gold substrates has been studied by Spectroscopic Ellipsometry (SE) in the 245-1000 nm wavelength range. The investigation has been performed in aqueous ambient at room temperature, focusing on monolayer-thick films. In situ δΨ and δΔ difference spectra have shown reproducibly well-defined features related to molecular optical absorptions typical of the so-called heme group. The data have been reproduced quantitatively by a simple isotropic optical model, accounting for the molecular absorption spectrum and film-substrate interface effects. The simulations allowed a reliable estimate of the film thickness and the determination of the position and the shape of the so-called Soret absorption peak that, within the experimental uncertainty, is the same found for molecules in liquid. These findings suggest that YCC preserves its native structure upon adsorption. The same optical model was able to reproduce also ex situ results on rinsed and dried samples, dominated by the spectral features associated to the polypeptide chain that tend to overwhelm the heme absorption features.