Preparation and characterization of Thioflavin T doped silica nanoparticles

Fluorescent silica nanoparticles with diameters of about 300 nm were synthesized based on Stöber´s method, using Thioflavin T as fluorescent co-reagent. The particles were characterized via transmission electron microscopy and fluorimetry measurements. Fluorescence intensity of the sols was ten times higher than that of the ethanol phase solutions of Thioflavin T. Release of dye molecules in stable alcosols was investigated by measuring UV-Vis absorbance spectrum of the supernatant. To try an alternative route, we investigated accumulation of dye molecules in native silica particles. No release effect was detected, and slow accumulation was observed. Water contact angles of the particles were assessed from analyzing the Langmuir films, and were found to be 18\r , very similar to native silica particles. Langmuir-Blodgett films of the particles were deposited on a glass substrate and were examined via UV-Vis spectrophotometry, fluorimetry and scanning electron microscopy. Presence of the film was revealed; the particles formed a continuous, well-packed monolayer

The supramolecular chemistry of gold and l-cysteine: Formation of photoluminescent, orange-emitting assemblies with multilayer structure

The protein mediated approach is a common method for the synthesis of photoluminescent gold quantum clusters (GQCs), where proteins, acting as reducing and stabilizing agents, react with gold salts through cysteine residues. For the better understanding of the phenomenon, the aqueous phase reaction of HAuCl_4 and L-cysteine has been investigated at the supramolecular level by various experimental techniques and molecular mechanics simulations. We have observed the formation of a novel photoluminescent product, (AuCys)_n^β, which shows emission in the orange region of the spectrum. Small- and wide-angle X-ray scattering (SWAXS) measurements have revealed the presence of nanosized lamellae, which have an internal multilayer superlattice structure with a characteristic periodic distance of 1.3 nm. Based on the results, the layers are built up by zigzag shaped (AuCys)_n polymer chains connected through aurophilic bonds. The aurophilic network is stabilized via salt bridges and hydrogen bonds, which are also responsible for the interlayer interactions. Here, the evolution of the multilayer structure has been monitored by the combined application of photoluminescence spectroscopy and time-resolved SAXS. It has been concluded that there is a strong correlation between the emission and the scattering intensity, which suggests that the two- and three-dimensional aggregation of the building blocks to form sheets and multilayers are simultaneous processes. Furthermore, we have revealed that the formation and behavior of (AuCys)_n^β show significant differences to that of Au-L-glutathione compounds desrcibed earlier despite the similarity of L-cysteine and L-glutathione. These results evidence that L-cysteine and gold species form building blocks that can be applied expansively in supramolecular and cluster chemistry

Intercalation of Bovine Serum Albumin Coated Gold Clusters Between Phospholipid Bilayers: Temperature-Dependent Behavior of Lipid-AuQC@BSA Assemblies with Red Emission and Superlattice Structure

A method has been developed to encapsulate bovine serum albumin (BSA)-coated gold quantum clusters (AuQC@BSA) in a multilamellar system of dipalmitoylphosphatidylcholine (DPPC). Results have shown that intercalation of AuQC@BSA particles into lipid bilayers occurs in the presence of CaCl2. Intense red photoluminescence emission was observed after encapsulation of the clusters. A well-defined structure was found with periodic distances drastically larger than that in the pure DPPC/water system. Although Ca2+ ions can change the dipole characteristics of the lipid bilayer surface, leading to unbinding between the bilayers of multilamellar DPPC/water system, the repulsion is shielded in the presence of AuQC@BSA particles. A coherent superlattice structure evolves due to mixed Ca2+-DPPC and Ca2+-AuQC@BSA interactions. Studies at different temperatures have suggested a correlation between the luminescence properties of the clusters and phase transition of the lipid layers. The temperature-dependent behavior assumes the connection between the coating and the lipid bilayer surface. Temperature-dependent features of lipid intercalated Au clusters provide new opportunities in their application