Marco Litschauer

Polarization sensitive optical coherence tomography of melanin provides intrinsic contrast based on depolarization

Polarization sensitive optical coherence tomography (PS-OCT) is a functional extension of OCT. In addition to imaging based on tissue reflectivity, PS-OCT also enables depth-resolved mapping of sample polarization properties such as phase-retardation, birefringent axis orientation, Stokes vectors, and degree of polarization uniformity (DOPU). In this study, PS-OCT was used to investigate the polarization properties of melanin. In-vitro measurements in samples with varying melanin concentrations revealed polarization scrambling, i.e. depolarization of backscattered light. Polarization scrambling in the PS-OCT images was more pronounced for higher melanin concentrations and correlated with the concentration of the melanin granules in the phantoms. Moreover, in-vivo PS-OCT was performed in the retinas of normal subjects and individuals with albinism. Unlike in the normal eye, polarization scrambling in the retinal pigment epithelium (RPE) was less pronounced or even not observable in PS-OCT images of albinos. These results indicate that the depolarizing appearance of pigmented structures like, for instance, the RPE is likely to be caused by the melanin granules contained in these cells.

Nanoparticles connected through an ionic liquid-like network

Silica nanoparticles linked through ionic liquid-like molecules are synthesized by two routes. The first approach utilized a bis(trialkoxysilyl)-substituted imidazolium iodide to link the silica nanoparticles. In the second approach, the silica nanoparticles were first modified by 3-chloropropyltrimethoxysilane and N-(3-trimethoxysilylpropyl)imidazole and then coupled through nucleophilic substitution. A comparison of both approaches shows that the second approach results in a more efficient interfacing of nanoparticles.

Confinement of 1-butyl-3-methylimidazolium nitrate in metallic silver.

The structure of the composite material consisting of the ionic liquid 1-butyl-3-methylimidazolium nitrate (BMINO3) entrapped in a silver matrix was investigated. Entrapment is confirmed by combining thermal analysis and spectroscopic investigations and by comparing physicochemical properties of the genuine ionic liquid and the composite BMINO3@Ag. An organization of the ionic liquid molecules toward the silver surface was observed.

Photoluminescence as Complementary Evidence for Short-Range Order in Ionic Silica Nanoparticle Networks.

Recently we published the synthesis of new hybrid materials, ionic silica nanoparticles networks (ISNN), made of silica nanoparticles covalently connected by organic bridging ligands containing imidazolium units owing to a “click-chemistry-like” reaction. Among other techniques small-angle X-ray scattering (SAXS) experiments were carried out to get a better picture of the network extension. It turned out that the short-range order in ISNN materials was strongly influenced by the rigidity of the bridging ligand, while the position of the short-range order peaks confirmed the successful linking of the bridging ligands. The photoluminescence experiments reported in this communication revealed strongly enhanced emission in the hybrid material in comparison with neat imidazolium salts. Moreover the shift of the emission maximum toward longer wavelengths, obtained when varying the aromatic ring content of the bridging ligand, suggested the existence of strong π−π stacking in the hybrid material. Experiments revealed a stronger luminescence in those samples exhibiting the higher extent of short-range order in SAXS.

Exploring the Molecular Structure of Imidazolium–Silica-Based Nanoparticle Networks by Combining Solid-State NMR Spectroscopy and First-Principles Calculations

A DFT-based molecular model for imidazolium-silica-based nanoparticle networks (INNs) is presented. The INNs were synthesized and characterized by using small-angle X-ray scattering (SAXS), NMR spectroscopy, and theoretical ab initio calculations. (11)B and (31)P HETCOR CP MAS experiments were recorded. Calculated (19)F NMR spectroscopy results, combined with the calculated anion-imidazolium (IM) distances, predicted the IM chain density in the INN, which was also confirmed from thermogravimetric analysis/mass spectrometry results. The presence of water molecules trapped between the nanoparticles is also suggested. First considerations on possible π-π stacking between the IM rings are presented. The predicted electronic properties confirm the photoluminescence emissions in the correct spectral domain.

Porous titania ionic nanoparticle networks.

Titania nanoparticle networks were synthesized by the reaction between imidazole and alkyl halide functionalized anatase nanoparticles. The reaction produced imidazolium bridging units between the nanoparticles that were observed by the means of CP MAS (15)N NMR spectroscopy. The porous characteristics of the obtained nanoparticle network were investigated with nitrogen sorption experiments. From these experiments, a high surface area originating from small mesopores was observed. These results were confirmed by small-angle X-ray diffraction experiments.

Entrapment of an Ionic Liquid in a Metallic Silver Matrix through Precipitation

Entrapment of an ionic liquid within metallic silver by means of physical caging is described. Thermal analysis of this new silver-based composite material allows estimation of the 1-butyl-3-methylimidazolium nitrate entrapment efficiency at 98%.

Ionic bis-nanoparticle networks

A newly arising challenge in the field of nanoparticle research concerns the control and the understanding of the interparticle interactions and interparticle properties. This should allow the development of materials based on nanoparticle assemblies which represents a great opportunity to exploit nanoparticle collective properties. Although some nanoparticle networks have been reported, few works are addressing the highly exciting problem of forming bis-nanoparticle assemblies in which two different types of nanoparticles are present. In this article we report an original synthesis pathway for the formation of an ionic bis-nanoparticle network, silica/silver, based on the formation of an imidazolium bridging unit. The reaction used for the formation of the bridging imidazolium can be considered as click-like chemistry. The synthesis of the metal/metal oxide hybrid composite material starts from the formation of a metal oxide nanoparticle modified with an imidazole ligand. This composite formation is therefore very general and could be extended to other metal/metal oxide composites.Graphical Abstract.

Tuning the Pore Size in Ionic Nanoparticle Networks

Highly promising hybrid materials consisting of silica, titania, or zirconia nanoparticles linked with ionic liquid-like imidazolium units have been developed. The nanoparticle networks are prepared by click-chemistry-like process through a nucleophilic substitution reaction. The type of metal oxide nanoparticles appears to play a key role regarding the pore size of the hybrid material.