Ultrathin gold films prepared by evaporation of sub-percolation layers (typically up to 10 nm nominal thickness) onto transparent substrates form arrays of well-defined metal islands. Such films display a characteristic surface plasmon (SP) absorption band, conveniently measured by transmission spectroscopy. The SP band intensity and position are sensitive to the film morphology (island shape and inter-island separation) and the effective dielectric constant of the surrounding medium. The latter has been exploited for chemical and biological sensing in the transmission localized surface plasmon resonance (T-LSPR) mode. A major concern in the development of T-LSPR sensors based on Au island films is instability, manifested as change in the SP absorbance following immersion in organic solvents and aqueous solutions. The latter may present a problem in the use of Au island-based transducers for biological sensing, usually carried out in aqueous media. Here, we describe a facile method for stabilizing Au island films while maintaining a high sensitivity of the SP absorbance to analyte binding. Stabilization is achieved by coating the Au islands with an ultrathin silica layer, ca. 1.5 nm thick, deposited by a sol-gel procedure on an intermediate mercaptosilane monolayer. The silica coating is prepared using a modified literature procedure, where a change in the reaction conditions from room temperature to 90 degrees C shortened the deposition time from days to hours. The system was characterized by UV-vis spectroscopy, ellipsometry, XPS, HRSEM, AFM, and cyclic voltammetry. The ultrathin silica coating stabilizes the optical properties of the Au island films toward immersion in water, phosphate buffer saline (PBS), and various organic solvents, thus providing proper conditions where the optical response is sensitive only to changes in the effective dielectric constant of the immediate environment. The silica layer is thin enough to afford high T-LSPR sensitivity, while the hydroxyl groups on its surface enable chemical modification for binding of receptor molecules. The use of silica-encapsulated Au island films as a stable and effective platform for T-LSPR sensing is demonstrated.

Electron microscopy (EM) of fully wet samples is a valuable tool for studies in the material, medical and biological sciences. In order to appreciate the natural structures of tissues or materials they should be examined in their native wet state, as opposed to a dry form that incorporates artifacts of sample processing. Viewing and analyzing wet samples at high resolution has undergone a significant improvement only recently due to the innovative WETSEMTM technology developed by QuantomiX.

CdSe nanoparticles were electrodeposited on mechanically strained gold, the latter achieved by controlled bending of gold films evaporated on mica. It is shown that the size and bandgap of the electrodeposited CdSe quantum dots (QDs) can be varied by applying mechanical strain to the Au substrate during deposition. This is attributed to change in the lattice spacing of the strained {111} Au and consequently in the lattice mismatch between the Au and the CdSe. Negative mechanical strain promotes the formation of rocksalt (RS) CdSe nanocrystals, normally existing only at high pressures. This is attributed to surface tension compression in the small crystals, together with enhancement of the phase transition by the CdSe/substrate interface.

Semiconductor nanocrystals can be epitaxially electrodeposited onto single-crystal substrates. The lateral size of the nanocrystals was previously shown to be controlled mainly by the lattice mismatch between the substrate and semiconductor. Here we show that, although the lateral dimensions of the nanocrystals are only slightly dependent on the current density and temperature of deposition, the vertical dimension is strongly dependent on these parameters. This allows control of the shape and aspect ratio of the nanocrystals, from spherical at high deposition current to taller crystals with a shape between columnar and square pyramidal with rounded tops at low currents. The shape of the taller crystals is explained by considering the reduced role of kinetic factors at low current density. Cross-sectional TEM is used to image the nanoparticle shape, while photoelectrochemical spectral measurements allow approximate band gap values to be estimated for the various nanocrystals.