Donnan Permselectivity in Layer-by-Layer Self-Assembled Redox Polyelectrolye Thin Films

Redox polyelectrolyte multilayers have been assembled with use of the layer-by-layer (LBL) deposition technique with cationic poly(allylamine) modified with Os(bpy)2ClPyCHO (PAH-Os) and anionic poly(styrene)sulfonate (PSS) or poly(vinyl)sulfonate (PVS). Different behavior has been observed in the formal redox potential of the Os(II)/Os(III) couple in the polymer film with cyclic voltammetry depending on the charge of the outermost layer and the electrolyte concentration and pH. The electrochemical quartz crystal microbalance (EQCM) has been used to monitor the exchange of ions and solvent with the external electrolyte during redox switching. At low ionic strength Donnan permselectivity of anions or cations is apparent and the nature of the ion exclusion from the film is determined by the charge of the topmost layer and solution pH. At high electrolyte concentration Donnan breakdown is observed and the osmium redox potential approaches the value for the redox couple in solution. Exchange of anions and water with the external electrolyte under permselective conditions and salt and water under Donnan breakdown have been observed upon oxidation of the film at low pH for the PAH-Os terminating layer. Moreover, at high pH values and with PVS as the terminating layer EQCM mass measurements have shown that cation release was masked by water exchange

Double Direct Templating of Periodically Nanostructured ZnS Hollow Microspheres

We introduce a “double direct templating” method for obtaining hollow microspheres with periodically nanostructured walls. Silica or polystyrene colloids are dispersed in a self-assembled hexagonal lyotropic liquid crystal containing precursors for ZnS. The semiconductor ZnS mineralizes on the surface of the colloid, expressing a pore morphology that is a copy of the structure of the liquid crystal. After etching of the sacrificial colloids, hollow capsules with templated and uniform mesoporous shells are obtained

Photoactive Red Fluorescent SiO₂ Nanoparticles Based on Controlled Methylene Blue Aggregation in Reverse Microemulsions

We present a reverse microemulsion synthesis procedure for incorporating methylene blue (MB), a known FDA-approved type-II red-absorbing photosensitizer and 1O2 generator, into the matrix of hydrophobic-core/hydrophilic-shell SiO2 nanoparticles. Different synthesis conditions were explored with the aim of controlling the entrapped-dye aggregation at high dye loadings in the hydrophobic protective core; minimizing dye aggregation ensured highly efficient photoactive nanoentities for 1O2 production. Monitoring the synthesis in real time using UV–vis absorption allowed tracking of the dye aggregation process. In particular, silica nanoparticles (MB@SiO2 NPs) of ∼50 nm diameter size with a high local entrapped-MB concentration (∼10–2 M, 1000 MB molecules per NP) and a moderate proportion of dye aggregation were obtained. The as-prepared MB@SiO2 NPs showed a high singlet oxygen photogeneration efficiency (ΦΔ = 0.30 ± 0.05), and they can be also considered as red fluorescent probes (ΦF ∼ 0.02, λmax ∼ 650 nm). The distinctive photophysical and photochemical characteristics of the synthesized NPs reveal that the reverse microemulsion synthesis procedure offers an interesting strategy for the development of complex theranostic nano-objects for photodynamic therapy

Mesoporous ZnS Thin Films Prepared by a Nanocasting Route

Mesoporous metal chalcogenides (e.g., ZnS, CuS, and derived mixed sulfide or selenides) show an extremely high potential in technological areas like catalysis, sensors, environmental protection, and photovoltaics. Although chemical bath deposition methods allow obtaining stable and porous metal chalcogenide films under mild and simple conditions, the reproducible preparation of highly ordered mesoporous sulfide thin films has been challenging so far. Herein, we present a simple and efficient synthetic method to prepare ZnS mesoporous thin films using a combination of a nanocasting approach and a successive ionic layer adsorption and reaction (SILAR) process for the infiltration. A mesoporous silica thin film, prepared by evaporation induced self-assembly (EISA), serves as the hard exotemplate for the formation of the mesostructured zinc sulfide. After selective etching of the silica framework, a stable and porous ZnS thin film is obtained, which replicates the pore structure of the hard template. A thorough combination of characterization techniques is used to assess the exotemplating process as well as the template removal

Silver Nanoparticle-Mesoporous Oxide Nanocomposite Thin Films: A Platform for Spatially Homogeneous SERS-Active Substrates with Enhanced Stability

We introduce a nanoparticle-mesoporous oxide thin film composite (NP-MOTF) as low-cost and straightforward sensing platforms for surface-enhanced Raman Spectroscopy (SERS). Titania, zirconia, and silica mesoporous matrices templated with Pluronics F-127 were synthesized via evaporation-induced self-assembly and loaded with homogeneously dispersed Ag nanoparticles by soft reduction or photoreduction. Both methods give rise to uniform and reproducible Raman signals using 4-mercaptopyridine as a probe molecule. Details on stability and reproducibility of the Raman enhancement are discussed. Extensions in the design of these composite structures were explored including detection of nonthiolated molecules, such as rhodamine 6-G or salicylic acid, patterning techniques for locating the enhancement regions and bilayered mesoporous structures to provide additional control on the environment, and potential size-selective filtration. These inorganic oxide–metal composites stand as extremely simple, reproducible, and versatile platforms for Raman spectroscopy analysis