Probing the rotational and translational diffusion and colloidal stability of nanorods is of significant fundamental interest with implications for many different applications. Recently R. Nixon-Luke and G. Bryant presented a...
Over
the last decade,
the interest in carbon dots, graphene dots,
or similar carbon-based nanoparticles has increased considerably.
This interest is based on potentially high fluorescent quantum yields,
controllable excitation-dependent emission, low toxicity, and convenient
reaction conditions. Carbon dots are often seen as a promising alternative
to classical semiconductor quantum dots that are typically made from
toxic semiconductor materials. Surprisingly, aspects like the atomic
structure, composition, mechanism of formation, and precise understanding
of the photophysical properties of carbon dots are still mostly unknown.
The large number of different precursor systems and the variety in
synthesis routes make a direct comparison of different systems difficult.
To advance this, we went for a systematic approach and compared the
results of four synthesis routes using two different precursor systems.
We used different spectroscopy and microscopy methods including fluorescence
correlation spectroscopy to characterize the different reaction products.
We found that for syntheses solely based on citric acid as the precursor,
we obtain particles where the emission wavelength is strongly dependent
on the excitation wavelength despite relatively low quantum yields.
In comparison, when urea is added as a nitrogen doping reactant, we
observe vastly increased quantum yields. By making use of a combination
of dialysis and column chromatography, we were able to isolate various
luminescent species with high quantum yields and verify the existence
of different molecular fluorophores. A detailed and consistent characterization
of the reaction products during the course of purification revealed
strong interactions between molecular fluorophores and larger reaction
products.
Stabilization of
gold nanoparticles in organic solvents is a key
challenge in making them available for a wider range of material applications.
Polymers are often used as stabilizing ligands because they also allow
for the introduction of new properties and functionalities. Many of
the established synthesis protocols for gold nanoparticles are water-based.
However, the insolubility of many synthetic polymers in water renders
the direct functionalization of aqueous particle dispersions with
these ligands difficult. Here, we report on an approach for the functionalization
of gold nanoparticles, which were prepared by aqueous synthesis, with
hydrophobic polymer ligands and their characterization in nonpolar,
organic dispersions. Our method employs an auxiliary ligand to first
transfer gold nanoparticles from an aqueous to an organic medium.
In the organic phase, the auxiliary ligand is then displaced by thiolated
polystyrene ligands to form a dense polymer brush on the particle
surface. We characterize the structure of the ligand shell using electron
microscopy, scattering techniques, and ultracentrifugation and analyze
the influence of the molecular weight of the polystyrene ligands on
the structure of the polymer brush. We further investigate the colloidal
stability of polystyrene-functionalized gold nanoparticles in various
organic solvents. Finally, we extend the use of our protocol from
small, spherical gold nanoparticles to larger gold nanorods and nanocubes.
We present the synthesis of so called amphiphilic glycomacromolecules (APGs) by using solid-phase polymer synthesis. Based on tailor made building blocks, monosdisperse APGs with varying compositions are synthesized, introducing carbohydrate...
Magnetic nanoparticles (MNPs) are widely known as valuable agents for biomedical applications. Recently, MNPs were further suggested to be used for a remote and non-invasive manipulation, where their spatial redistribution or force response in a magnetic field provides a fine-tunable stimulus to a cell. Here, we investigated the properties of two different MNPs and assessed their suitability for spatio-mechanical manipulations: semisynthetic magnetoferritin nanoparticles and fully synthetic ‘nanoflower’-shaped iron oxide nanoparticles. As well as confirming their monodispersity in terms of structure, surface potential, and magnetic response, we monitored the MNP performance in a living cell environment using fluorescence microscopy and asserted their biocompatibility. We then demonstrated facilitated spatial redistribution of magnetoferritin compared to ‘nanoflower’-NPs after microinjection, and a higher magnetic force response of these NPs compared to magnetoferritin inside a cell. Our remote manipulation assays present these tailored magnetic materials as suitable agents for applications in magnetogenetics, biomedicine, or nanomaterial research.
Amphiphilic glycan-functionalized oligomers are derived by solid-phase polymer synthesis and applied in both, self-assembled micelles as well as giant unilamellar vesicles, as simplified models of the cell's glycocalyx. Additionally, an aggregation-induced luminophore is introduced into the amphiphilic glycomacromolecules showing no fluorescence when the molecule is free in solution. Combining glycomacromolecules carrying a binding glycan motif and the luminophore with glycomacromolecules or other amphiphiles with no binding motifs and no luminophore in self-assembled structures, micelles and vesicles exhibiting no or only very little fluorescence are obtained. Only upon clustering of the binding glycan motifs through interaction with a multivalent lectin receptor, an increase in fluorescence is observed. Thus, clustering events within these self-assembled structures can be detected and localized.
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