56 research outputs found

    Fluorescence Quenching of Tyrosine-Ag Nanoclusters by Metal Ions: Analytical and Physicochemical Assessment

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    A new synthesis method is described for the first time to produce silver nanoclusters (AgNCs) by using the tyrosine (Tyr) amino acid. Several important parameters (e.g., molar ratios, initial pH, reaction time etc.) were optimized to reach the highest yield. The formed Tyr-AgNCs show characteristic blue emission at őĽem = 410 nm, and two dominant fluorescence lifetime components were deconvoluted (ŌĄ1 ~ 3.7 and ŌĄ2 ~ 4.9 ns). The NCs contained metallic cores stabilized by dityrosine. For possible application, the interactions with several metal ions from the tap water and wastewater were investigated. Among the studied cations, four different ions (Cu2+, Ni2+, Fe3+, and Rh3+) had a dominant effect on the fluorescence of NCs. Based on the detected quenching processes, the limit of detection of the metal ions was determined. Static quenching (formation of a non-luminescent complex) was observed in all cases by temperature-dependent measurements. The calculated thermodynamic parameters showed that the interactions are spontaneous ranked in the following order of strength: Cu2+ > Fe3+ > Rh3+ > Ni2+. Based on the sign and relations of the standard enthalpy (őĒH¬į) and entropy changes (őĒS¬į), the dominant forces were also identified

    Optimization of dispersive liquid-liquid microextraction for polyethylene glycol-coated gold and silver nanoparticles

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    The use of polyethylene glycol modified nanoparticles is becoming an interesting topic since they present a very good stability in biological media. However, the effects of these nanoparticles on organisms are still unclear, so it is necessary to monitor their presence in bodily fluids, such as plasma or urine. Single-particle ICP-MS is a versatile tool to simultaneously detect and characterize nanoparticles in aqueous media, but a previous extraction step is necessary when analyzing complex samples due to the occurrence of matrix effects. In this work, an ultrasound assisted dispersive liquid-liquid microextraction method based on the use of chloroform as extracting solvent has been optimized for the extraction, characterization, and quantification of polyethylene glycol modified gold and silver nanoparticles in aqueous media. So far, we could achieve extraction efficiencies higher than 75% for both types of nanoparticles studied. We believe that with further optimization, the extraction can be made quantitative

    Fluorescent Labeling of Hyaluronic Acid-Chitosan Nanocarriers by Protein-Stabilized Gold Nanoclusters

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    In medical research the visualization of drug carrier accumulation and release of the loaded drugs in vivo is an important field. In this work, two protein-stabilized gold nanoclusters (Au NCs) as effective fluorescent reporters (FRs) were investigated for labeling of biocompatible chitosan-modified hyaluronic acid based nanocarriers having two different structures. The colloid stability of the labeled carriers was studied by dynamic light scattering and Zeta potential measurements, while the changes in the fluorescence of the lysozyme- (LYZ) and bovine serum albumin (BSA)-stabilized Au NCs were analyzed by spectrofluorimetry and confocal fluorescent microscopy. We found that the labeling was effective with a wide range of marker:carrier mass ratios, and the fluorescence of the NCs and the colloid stability of the complexes were retained. Labeling during preparation and subsequent labeling were compared, and based on composition (nanocluster:carrier mass ratio) and structure of the complex systems we preferred the latter method, as it left the Au NCs free for further modifications. Considering both marker:carrier mass ratios and emission intensities, the LYZ-stabilized Au NCs proved to be better labels. The core-shell type carrier formulations showed increased fluorescence with LYZ-stabilized NCs, presumably from aggregation induced emission

    Promising Bioactivity of Vitamin B1-Au Nanocluster: Structure, Enhanced Antioxidant Behavior, and Serum Protein Interaction

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    In the current work, we first present a simple synthesis method for the preparation of novel Vitamin-B1-stabilized few-atomic gold nanoclusters with few atomic layers. The formed nanostructure contains ca. eight Au atoms and shows intensive blue emissions at 450 nm. The absolute quantum yield is 3%. The average lifetime is in the nanosecond range and three main components are separated and assigned to the metal‚Äďmetal and ligand‚Äďmetal charge transfers. Based on the structural characterization, the formed clusters contain Au in zero oxidation state, and Vitamin B1 stabilizes the metal cores via the coordination of pyrimidine-N. The antioxidant property of the Au nanoclusters is more prominent than that of the pure Vitamin B1, which is confirmed by two different colorimetric assays. For the investigation into their potential bioactivity, interactions with bovine serum albumin were carried out and quantified. The determined stoichiometry indicates a self-catalyzed binding, which is almost the same value based on the fluorometric and calorimetric measurements. The calculated thermodynamic parameters verify the spontaneous bond of the clusters along the protein chain by hydrogen bonds and electrostatic interactions
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