Most bacteria in nature exist as biofilms, which support intercellular signaling processes such as quorum sensing (QS), a cell-to-cell communication mechanism that allows bacteria to monitor and respond to cell density and changes in the environment. Because QS and biofilms are involved in the ability of bacteria to cause disease, there is a need for the development of methods for the non-invasive analysis of QS in natural bacterial populations. Here, by using surface-enhanced resonance Raman scattering spectroscopy, we report rationally designed nanostructured plasmonic substrates for the in-situ, label-free detection of a QS signaling metabolite in growing Pseudomonas aeruginosa biofilms and microcolonies. The in situ, non-invasive plasmonic imaging of QS in biofilms provides a powerful analytical approach for studying intercellular communication on the basis of secreted molecules as signals.

Hybrid colloids consisting of noble metal cores and metal oxide shells have been under intense investigation for over two decades and have driven progress in diverse research lines including sensing, medicine, catalysis, and photovoltaics. Consequently, plasmonic core-shell particles have come to play a vital role in a plethora of applications. Here, an overview is provided of recent developments in the design and utilization of the most successful class of such hybrid materials, silica-coated plasmonic metal nanoparticles. Besides summarizing common simple approaches to silica shell growth, special emphasis is put on advanced synthesis routes that either overcome typical limitations of classical methods, such as stability issues and undefined silica porosity, or grant access to particularly sophisticated nanostructures. Hereby, a description is given, how different types of silica can be used to provide noble metal particles with specific functionalities. Finally, applications of such nanocomposites in ultrasensitive analyte detection, theranostics, catalysts, and thin-film solar cells are reviewed.

Noble metal nanoparticles are widely used as probes or substrates for surface enhanced Raman scattering (SERS), due to their characteristic plasmon resonances in the visible and near-IR spectral ranges. Aiming at obtaining a versatile system with high SERS performance, we developed the synthesis of quasi-monodisperse, nonaggregated gold nanoparticles protected by radial mesoporous silica shells. The radial mesoporous channels were used as templates for the growth of gold tips branching out from the cores, thereby improving the plasmonic performance of the particles while favoring the localization of analyte molecules at high electric field regions: close to the tips, inside the pores. The method, which additionally provides control over tip length, was successfully applied to gold nanoparticles with various shapes, leading to materials with highly efficient SERS performance. The obtained nanoparticles are stable in ethanol and water upon thermal consolidation and can be safely stored as a powder.

High-pressure optical-absorption measurements performed in CuWO(4) up to 20 GPa provide experimental evidence of the persistence of the Jahn-Teller (JT) distortion in the whole pressure range both in the low-pressure triclinic and in the high-pressure monoclinic phase. The electron-lattice couplings associated with the e(g)(E⊗e) and t(2g)(T⊗e) orbitals of Cu(2+) in CuWO(4) are obtained from correlations between the JT distortion of the CuO(6) octahedron and the associated structure of Cu(2+) d-electronic levels. This distortion and its associated JT energy (E(JT)) decrease upon compression in both phases. However, both the distortion and associated E(JT) increase sharply at the phase-transition pressure (P(PT)=9.9 GPa), and we estimate that the JT distortion persists for a wide pressure range not being suppressed up to 37 GPa. These results shed light on the transition mechanism of multiferroic CuWO(4), suggesting that the pressure-induced structural phase transition is a way to minimize the distortive effects associated with the toughness of the JT distortion.

The internal organization of gold nanorod supercrystals is fully described as well as infiltration with silica and SERS performance.

We describe the preparation of multibranched gold−silica−molecularly imprinted polymer (bAu@mSiO 2 @ MIP) core−shell nanoparticles, with their specific ability to recognize enrofloxacin (ENRO), and their application as labelfree nanosensors for the specific detection of the antimicrobial by surface-enhanced Raman scattering. The use of these nanocomposites results in a large enhancement of the Raman scattering of ENRO upon binding of an antibiotic to the selective recognition sites in the MIP. These are in the proximity of the gold core branches that act as intrinsic hot spots providing highly localized and strongly enhanced electromagnetic fields caused by plasmon resonance. The effect of the multibranched morphology of the gold cores (bAu) on the optical spectroscopic response of the bAu@mSiO 2 @MIP nanosensors is investigated with the aim of improving ENRO detection. The optimized nanostructures allowed us to achieve a detection limit of 1.5 nM for ENRO, which is 2 orders of magnitude lower than those for previously reported Au@MIP nanosensors, additionally providing negligible cross-reactivity toward other potential interfering species.

We report a complete structural study of CoF 2 under pressure. Its crystal structure and vibrational and electronic properties have been studied both theoretically and experimentally using first-principles density functional theory (DFT) methods, x-ray diffraction, x-ray absorption at Co K-edge experiments, Raman spectroscopy, and optical absorption in the 0-80 GPa range. We have determined the structural phase-transition sequence in CoF 2 and corresponding transition pressures. The results are similar to other transition-metal difluorides such as FeF 2 but different to ZnF 2 and MgF 2 , despite that the Co 2+ size (ionic radius) is similar to Zn 2+ and Mg 2+ . We found that the complete phase-transition sequence is tetragonal rutile (P 4 2 /mnm) → CaCl 2 type (orthorhombic P nnm) → distorted PdF 2 (orthorhombic P bca) + PdF 2 (cubic P a3) in coexistence → fluorite (cubic F m3m) → cotunnite (orthorhombic P nma). It was observed that the structural phase transition to the fluorite at 15 GPa involves a drastic change of coordination from sixfold octahedral to eightfold cubic with important modifications in the vibrational and electronic properties. We show that the stabilization of this high-pressure cubic phase is possible under nonhydrostatic conditions since ideal hydrostaticity would stabilize the distorted-fluorite structure (tetragonal I 4/mmm) instead. Although the first rutile → CaCl 2 -type second-order phase transition is subtle by Raman spectroscopy, it was possible to define it through the broadening of the E g Raman mode which is split in the CaCl 2 -type phase. First-principles DFT calculations are in fair agreement with the experimental Raman mode frequencies, thus providing an accurate description for all vibrational modes and elastic properties of CoF 2 as a function of pressure.

Hybrid colloids consisting of noble metal cores and metal oxide shells have been under intense investigation for over two decades and have driven progress in diverse research lines including sensing, medicine, catalysis, and photovoltaics. Consequently, plasmonic core-shell particles have come to play a vital role in a plethora of applications. We provide in this review an overview of recent developments in the design and utilization of the most successful class of such hybrid materials: silica-coated plasmonic metal nanoparticles. Besides summarizing common simple approaches to silica shell growth, special emphasis is put on advanced synthesis routes that either overcome typical limitations of classical methods, such as stability issues and undefined silica porosity, or grant access to particularly sophisticated nanostructures. We hereby describe how different types of silica can be used to provide noble metal particles with specific functionalities and review applications of such nanocomposites in ultrasensitive analyte detection, theranostics, catalysts, and thin film solar cells.Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff)) Published online: ((will be filled in by the editorial staff)) Metal/silica nanocomposites have been under intensive investigation for over 20 years.Besides the development of a wide array of synthesis strategies for the preparation of highly regular hybrid plasmonic nanoparticles, a considerable number of practical applications have been presented in sensing, theranostics, catalysis, and photovoltaics. Herein, an overview of the recent advances in the design and utilization of such materials is provided.