13 research outputs found
Core-Shell Structure of Monodisperse Poly(ethylene glycol)-Grafted Iron Oxide Nanoparticles Studied by Small-Angle X-ray Scattering
The promising applications of core-shell nanoparticles in the biological and medical field have been well investigated in recent years. One remaining challenge is the characterization of the structure of the hydrated polymer shell. Here we use small-angle X-ray scattering (SAXS) to investigate iron oxide core-poly(ethylene glycol) brush shell nanoparticles with extremely high polymer grafting density. It is shown that the shell density profile can be described by a scaling model that takes into account the locally very high grafting density near the core. A good fit to a constant density region followed by a star-polymer-like, monotonously decaying density profile is shown, which could help explain the unique colloidal properties of such densely grafted core-shell nanoparticles. SAXS experiments probing the thermally induced dehydration of the shell and the response to dilution confirmed that the observed features are associated with the brush and not attributed to structure factors from particle aggregates. We thereby demonstrate that the structure of monodisperse core-shell nanoparticles with dense solvated shells can be well studied with SAXS and that different density models can be distinguished from each other. (Graph Presented)
Monodisperse Iron Oxide Nanoparticles by Thermal Decomposition: Elucidating Particle Formation by Second-Resolved in Situ Small-Angle X‑ray Scattering
The
synthesis of iron oxide nanoparticles (NPs) by thermal decomposition
of iron precursors using oleic acid as surfactant has evolved to a
state-of-the-art method to produce monodisperse, spherical NPs. The
principles behind such monodisperse syntheses are well-known: the
key is a separation between burst nucleation and growth phase, whereas
the size of the population is set by the precursor-to-surfactant ratio.
Here we follow the thermal decomposition of iron pentacarbonyl in
the presence of oleic acid via in situ X-ray scattering. This method
allows reaction kinetics and precursor states to be followed with
high time resolution and statistical significance. Our investigation
demonstrates that the final particle size is directly related to a
phase of inorganic cluster formation that takes place between precursor
decomposition and particle nucleation. The size and concentration
of clusters were shown to be dependent on precursor-to-surfactant
ratio and heating rate, which in turn led to differences in the onset
of nucleation and concentration of nuclei after the burst nucleation
phase. This first direct observation of prenucleation formation of
inorganic and micellar structures in iron oxide nanoparticle synthesis
by thermal decomposition likely has implications for synthesis of
other NPs by similar routes
Aligned multi-walled carbon nanotube-embodied hydrogel via low magnetic field:a strategy for engineering aligned injectable scaffolds
Abstract
Injectable scaffolds are a promising strategy to restore and regenerate damaged and diseased tissues. They require minimally invasive procedure and allow the formation of an in-situ structure of any shape. However, the formation of 3D in-situ structure with aligned morphologies using a method which could be easily transferred to clinical settings remains a challenge. Herein, the rational design of an aligned injectable hydrogel-based scaffold via remote-induced alignment is reported. Carboxylated multi-walled carbon nanotubes (cMWCNT) are aligned into hydrogel via low magnetic field. The uniform dispersion and alignment of cMWCNT into the hydrogel are clearly demonstrated by small angle neutron scattering. The obtained aligned cMWCNT-embodied hydrogel is stable over 7 days at room temperature and as well at body temperature (i.e. 37 °C). As unique approach, the formation of MWCNT-hydrogel composite is investigated combining rheology with molecular dynamic and quantum mechanical calculations. The increase of MWCNT concentration into the hydrogel decreases the total energy promoting structural stabilization and increase of stiffness. The remote aligning of injectable hydrogel-based scaffold opens up horizons in the engineering of functional tissues which requires specific cell orientation
Doping Method Determines Para- or Superparamagnetic Properties of Photostable and Surface-Modifiable Quantum Dots for Multimodal Bioimaging
Semiconductor
quantum dots (QDs) are widely used for optical applications
and bioimaging. In comparison to organic dyes used for fluorescent
labeling, QDs exhibit very high photostability and can be further
surface modified. Equipping QDs with magnetic properties (mQDs) makes
it possible to combine fluorescence and magnetic resonance imaging
analyses. For this purpose, we have prepared water-dispersible and
magnetic CdTe/ZnS mQDs, whereby ferrous ions are selectively incorporated
in either their cores or their shells. This study aims at understanding
the differences in optical, structural, and magnetic properties between
these core- and shell-doped mQDs. Field-dependent isothermal magnetic
susceptibility measurements show that shell-doped mQDs exhibit paramagnetic
and their core-doped equivalents superparamagnetic behavior
near room temperature. Shell doping results in about 1.7 times higher
photoluminescence quantum yields and 1.4 times higher doping efficiency
than core doping. X-ray diffraction patterns reveal that core doping
leads to defects in the lattice and hence to a severe decrease in
crystallinity, whereas shell doping has no significant impact on the
crystal structure and consequently fewer disadvantages regarding the
mQD’s quantum yield. These selective doping approaches, particularly
shell doping, allow for the tailored design of paramagnetic QDs having
modifiable and biocompatible particle surfaces. The organic ligandsin
this study <i>N</i>-acetyl-l-cysteinesufficiently
prevent leakage of toxic metal ions, as shown by cytotoxicity assays
with HepG2 cells. Confocal laser scanning microscopy shows that mQDs
are internalized by these cells and accumulated near their nuclei.
This study shows that biocompatible, fluorescent, and paramagnetic
QDs are promising photostable labels for multimodal bioimaging