Fluorescence detection system based on silicon quantum dots–polysilane nanocomposites

A dual channel fluorescence system that combines the optical properties of silicon quantum dots–polysilane nanocomposites with those of 2-(4-chlorophenyl)-6-(thiophen-2-yl)pyridine, a fluorescent cytotoxic agent, is presented. The system is capable to alternatively trigger emission signals at two different wavelengths by excitation at a single wavelength. For this purpose a highly stable colloidal dispersion of silicon quantum dots–polysilane nanocomposite is prepared by a one-pot synthetic method using microwave-activated Wurtz coupling of organochlorosilanes. The size and shape of the silicon quantum dots within the polysilane thin film are studied by TEM. The colloidal dispersions are investigated by SAXS, which evidences that polysilane plays also a role as stabilizing agent to prevent aggregation. UV-vis spectrophotometry of the silicon quantum dots–polysilane nanocomposites in the presence of 2-(4-chlorophenyl)-6-(thiophen-2-yl)pyridine is used to define the active wavelength range and establish the fluorescence detection method

The influence of polysilane chemical structure on optical properties, rubbed film morphology and LC alignment

Polysilane films were prepared by the drop casting method and their optical and morphological properties have been analyzed in order to investigate their suitability as alignment layers for nematic molecules. The samples do not absorb the radiations in the visible domain, particularly those containing methylhydrosilyl units, and present a transmittance of about 90% starting from 390 to 1100 nm. The optical band-gap is higher than 3.26 eV for all polysilanes indicating a low probability of optical absorption processes in the visible range. The morphology of the pristine samples shows isotropically distributed granular formations. The polymer surface was oriented by rubbing with two types of velvet: one with short fibers and the other with long fibers. The latter generates higher surface anisotropy, as shown by the reduction of the surface texture direction index values. The presence of methylhydrosilyl units allows a denser packing of the polymer structure and thus finer surface periodicities, leading to better orientation of the nematic molecules on the polysilane surface

Low-molecular-weight sulfonated chitosan as template for anticoagulant nanoparticles

Katja Heise,1,2 Mathias Hobisch,3,4 Liviu Sacarescu,5 Uros Maver,6 Josefine Hobisch,3 Tobias Reichelt,7 Marija Sega,6 Steffen Fischer,1 Stefan Spirk3,4 Members of EPNOE and NAWI Graz 1Institute of Plant and Wood Chemistry, Technische Universität Dresden, Tharandt, Germany; 2Department of Bioproducts and Biosystems, Aalto University, Espoo, Finland; 3Institute for Chemistry and Technology of Materials, Graz University of Technology, Graz, Austria; 4Institute for Paper, Pulp and Fiber Technology, Graz University of Technology, Graz, Austria; 5“Petru Poni” Institute of Macromolecular Chemistry, Romanian Academy, Iasi, Romania; 6Faculty of Medicine, University of Maribor, Maribor, Slovenia; 7Zentrum für Bucherhaltung GmbH, Leipzig, Germany Purpose: In this work, low-molecular-weight sulfoethyl chitosan (SECS) was used as a model template for the generation of silver core-shell nanoparticles with high potential as anticoagulants for medical applications. Materials and methods: SECS were synthesized by two reaction pathways, namely Michael addition and a nucleophilic substitution with sodium vinylsulfonate or sodium 2-bromoethanesulfonate (NaBES). Subsequently, these derivatives were used as reducing and capping agents for silver nanoparticles in a microwave-assisted reaction. The formed silver-chitosan core-shell particles were further surveyed in terms of their anticoagulant action by different coagulation assays focusing on the inhibition of either thrombin or cofactor Xa. Results: In-depth characterization revealed a sulfoalkylation of chitosan mainly on its sterically favored O6-position. Moreover, comparably high average degrees of substitution with sulfoethyl groups (DSSE) of up to 1.05 were realized in reactions with NaBES. The harsh reaction conditions led to significant chain degradation and consequently, SECS exhibits masses of <50 kDa. Throughout the following microwave reaction, stable nanoparticles were obtained only from highly substituted products because they provide a sufficient charge density that prevented particles from aggregation. High-resolution transmission electron microscopy images reveal that the silver core (diameter ~8 nm) is surrounded by a 1–2 nm thick SECS layer. These core-shell particles and the SECS itself exhibit an inhibiting activity, especially on cofactor Xa. Conclusion: This interesting model system enabled the investigation of structure–property correlations in the course of nanoparticle formation and anticoagulant activity of SECS and may lead to completely new anticoagulants on the basis of chitosan-capped nanoparticles. Keywords: chitosan ethylsulfonate, silver nanoparticles, antithrombotic activity, cofactor X