68 research outputs found
Growth mechanism of nanostructured superparamagnetic rods obtained by electrostatic co-assembly
We report on the growth of nanostructured rods fabricated by electrostatic
co-assembly between iron oxide nanoparticles and polymers. The nanoparticles
put under scrutiny, {\gamma}-Fe2O3 or maghemite, have diameter of 6.7 nm and
8.3 nm and narrow polydispersity. The co-assembly is driven by i) the
electrostatic interactions between the polymers and the particles, and by ii)
the presence of an externally applied magnetic field. The rods are
characterized by large anisotropy factors, with diameter 200 nm and length
comprised between 1 and 100 {\mu}m. In the present work, we provide for the
first time the morphology diagram for the rods as a function of ionic strength
and concentration. We show the existence of a critical nanoparticle
concentration and of a critical ionic strength beyond which the rods do not
form. In the intermediate regimes, only tortuous and branched aggregates are
detected. At higher concentrations and lower ionic strengths, linear and stiff
rods with superparamagnetic properties are produced. Based on these data, a
mechanism for the rod formation is proposed. The mechanism proceeds in two
steps : the formation and growth of spherical clusters of particles, and the
alignment of the clusters induced by the magnetic dipolar interactions. As far
as the kinetics of these processes is concerned, the clusters growth and their
alignment occur concomitantly, leading to a continuous accretion of particles
or small clusters, and a welding of the rodlike structure.Comment: 15 pages, 10 figures, one tabl
Poly(acrylic acid)-coated iron oxide nanoparticles : quantitative evaluation of the coating properties and applications for the removal of a pollutant dye
In this work, 6 to 12 nm iron oxide nanoparticles were synthesized and coated
with poly(acrylic acid) chains of molecular weight 2100 g/mol. Based on a
quantitative evaluation of the dispersions, the bare and coated particles were
thoroughly characterized. The number densities of polymers adsorbed at the
particle surface and of available chargeable groups were found to be 1.9 +/-
0.3 nm-2 and 26 +/- 4 nm-2, respectively. Occurring via a multi-site binding
mechanism, the electrostatic coupling leads to a solid and resilient anchoring
of the chains. To assess the efficacy of the particles for pollutant
remediation, the adsorption isotherm of methylene blue molecules, a model of
pollutant, was determined. The excellent agreement between the predicted and
measured amounts of adsorbed dyes suggests that most carboxylates participate
to the complexation and adsorption mechanisms. An adsorption of 830 mg/g was
obtained. This quantity compares well with the highest values available for
this dye.Comment: 14 pages 5 figures, accepted 06-Dec-2012; Journal of Colloid and
Interface Science (2013
Reorientation kinetics of superparamagnetic nanostructured rods
The attractive interactions between oppositely charged species (colloids,
macromolecules etc) dispersed in water are strong, and the direct mixing of
solutions containing such species generally yields to a precipitation, or to a
phase separation. We have recently developed means to control the
electrostatically-driven attractions between nanoparticles and polymers in
water, and at the same time to preserve the stability of the dispersions. We
give here an account of the formation of supracolloidal aggregates obtained by
co-assembly of 7 nm particles with copolymers. Nanostructured rods of length
comprised between 5 and 50 microns and diameter 500 nm were investigated. By
application of a magnetic field, the rods were found to reorient along with the
magnetic field lines. The kinetics of reorientation was investigated using step
changes of the magnetic field of amplitude 90 degrees. From the various results
obtained, among which an exponential decay of the tangent of the angle made
between the rod and the field, we concluded that the rods are
superparamagnetic.Comment: 12 pages - 452kB 7 - figures - 1 Table will be published in Journal
of Physics : Condensed Matte
Electrosteric enhanced stability of functional sub-10 nm cerium and iron oxide particles in cell culture medium
Applications of nanoparticles in biology require that the nanoparticles
remain stable in solutions containing high concentrations of proteins and
salts, as well as in cell culture media. In this work, we developed simple
protocols for the coating of sub-10 nm nanoparticles and evaluated the
colloidal stability of dispersions in various environments. Ligands (citric
acid), oligomers (phosphonate-terminated poly(ethylene oxide)) and polymers
(poly(acrylic acid)) were used as nanometer-thick adlayers for cerium (CeO2)
and iron (gamma-Fe2O3) oxide nanoparticles. The organic functionalities were
adsorbed on the particle surfaces via physical (electrostatic) forces.
Stability assays at high ionic strength and in cell culture media were
performed by static and dynamic light scattering. Among the three coating
examined, we found that only poly(acrylic acid) fully preserved the dispersion
stability on the long term (> weeks). The improved stability was explained by
the multi-point attachments of the chains onto the particle surface, and by the
adlayer-mediated electrosteric interactions. These results suggest that
anionically charged polymers represent an effective alternative to conventional
coating agents.Comment: 8 figures, 10 pages, 4 tables. to appear in Langmui
Universal scattering behavior of co-assembled nanoparticle-polymer clusters
Water-soluble clusters made from 7 nm inorganic nanoparticles have been
investigated by small-angle neutron scattering. The internal structure factor
of the clusters was derived and exhibited a universal behavior as evidenced by
a correlation hole at intermediate wave-vectors. Reverse Monte-Carlo
calculations were performed to adjust the data and provided an accurate
description of the clusters in terms of interparticle distance and volume
fraction. Additional parameters influencing the microstructure were also
investigated, including the nature and thickness of the nanoparticle adlayer.Comment: 5 pages, 4 figures, paper published in Physical Review
Electrostatic co-assembly of iron oxide nanoparticles and polymers : towards the generation of highly persistent superparamagnetic nanorods
A paradigm proposed recently by Boal et al. (A.K. Boal et al., Nature 404,
746-748, 2000) deals with the possibility to use inorganic nanoparticles as
building blocks for the design and fabrication of colloidal and supracolloidal
assemblies. It is anticipated that these constructs could be made of different
shapes, patterns and functionalities and could constitute the components of
future nanodevices including sensors, actuators or nanocircuits. Here we report
a protocol that allowed us to fabricate such nanoparticle aggregates. The
building blocks of the constructs were anionically coated iron oxide
nanocrytals (superparamagnetic, size 7 nm) and cationic-neutral block
copolymers. We have shown that the electrostatic interactions between charged
species can be controlled by tuning the ionic strength of the dispersion. Under
appropriate conditions, the control of electrostatics resulted in the
elaboration of spherical or elongated aggregates at the micrometer length
scale. The elongated aggregates were found to be rod-like, with diameters of a
few hundred nanometers and lengths between 1 and 50 micrometers. In addition to
their remarkable stiffness, the nanostructured rods were found to reorient
along with an externally applied magnetic field, in agreement with the laws of
superparamagnetism.Comment: 6 pages, 5 figures, appeared in Advanced materials in September 2008,
reference
In vitro toxicity and uptake of magnetic nanorods
In this paper we investigate the internalization and cytotoxicity of
nanostructured materials having the form of elongated rods, with diameter of
200 nm and lengths 1 - 10 {\mu}m. The rods were made from the controlled
aggregation of sub-10 nm iron oxide nanoparticles. Recently, we have shown that
the nanorods inherited the superparamagnetic property of the particles. These
rods can actually be moved by the application of an external magnetic field.
Here we evaluate the in vitro toxicity of the magnetic nanorods by using MTT
assays on NIH/3T3 mouse fibroblasts. The toxicity assays revealed that the
nanorods are biocompatible, as exposed cells remained 100% viable relative to
controls over a period of a few days. Optical microscopy allow to visualize the
rods inside the cells and to determine their number per cell. Roughly 1/3 of
the total incubated rods were uptaken by the fibroblasts.Comment: 8 pages, 5 figure
Interactions between Magnetic Nanowires and Living Cells : Uptake, Toxicity and Degradation
We report on the uptake, toxicity and degradation of magnetic nanowires by
NIH/3T3 mouse fibroblasts. Magnetic nanowires of diameters 200 nm and lengths
comprised between 1 {\mu}m and 40 {\mu}m are fabricated by controlled assembly
of iron oxide ({\gamma}-Fe2O3) nanoparticles. Using optical and electron
microscopy, we show that after 24 h incubation the wires are internalized by
the cells and located either in membrane-bound compartments or dispersed in the
cytosol. Using fluorescence microscopy, the membrane-bound compartments were
identified as late endosomal/lysosomal endosomes labeled with lysosomal
associated membrane protein (Lamp1). Toxicity assays evaluating the
mitochondrial activity, cell proliferation and production of reactive oxygen
species show that the wires do not display acute short-term (< 100 h) toxicity
towards the cells. Interestingly, the cells are able to degrade the wires and
to transform them into smaller aggregates, even in short time periods (days).
This degradation is likely to occur as a consequence of the internal structure
of the wires, which is that of a non-covalently bound aggregate. We anticipate
that this degradation should prevent long-term asbestos-like toxicity effects
related to high aspect ratio morphologies and that these wires represent a
promising class of nanomaterials for cell manipulation and microrheology.Comment: 21 pages 12 figure
Parallelized Manipulation of Adherent Living Cells by Magnetic Nanoparticles-Mediated Forces
The remote actuation of cellular processes such as migration or neuronal outgrowth is a challenge for future therapeutic applications in regenerative medicine. Among the different methods that have been proposed, the use of magnetic nanoparticles appears to be promising, since magnetic fields can act at a distance without interactions with the surrounding biological system. To control biological processes at a subcellular spatial resolution, magnetic nanoparticles can be used either to induce biochemical reactions locally or to apply forces on different elements of the cell. Here, we show that cell migration and neurite outgrowth can be directed by the forces produced by a switchable parallelized array of micro-magnetic pillars, following the passive uptake of nanoparticles. Using live cell imaging, we first demonstrate that adherent cell migration can be biased toward magnetic pillars and that cells can be reversibly trapped onto these pillars. Second, using differentiated neuronal cells we were able to induce events of neurite outgrowth in the direction of the pillars without impending cell viability. Our results show that the range of forces applied needs to be adapted precisely to the cellular process under consideration. We propose that cellular actuation is the result of the force on the plasma membrane caused by magnetically filled endo-compartments, which exert a pulling force on the cell periphery
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