Low-temperature anomalies in muon spin relaxation of solid and hollow nanoparticles: a pathway to detect unusual local spin dynamics

By means of muon spin relaxation measurements we unraveled the temperature spin dynamics in monodisperse maghemite spherical nanoparticles with different surface to volume ratio, in two samples with a full core (diameter D∼4 and D∼5nm) and one with a hollow core (external diameter D∼7.4nm). The behavior of the muon longitudinal relaxation rates as a function of temperature allowed us to identify two distinct spin dynamics. The first is well witnessed by the presence of a characteristic peak for all the samples around the so-called muon blocking temperature T$_{B}^{μ+}$. A Bloembergen-Purcell-Pound (BPP)-like model reproduces the experimental data around the peak and at higher temperatures (20<T<100K) by assuming the Néel reversal time of the magnetization as the dominating correlation time. An additional dynamic emerges in the samples with higher surface to volume ratio, namely, full 4 nm and hollow samples. This is witnessed by a shoulder of the main peak for T<20K at low longitudinal field (μ$_{0}$H≈15mT), followed by an abrupt increase of the relaxation rate at T<10K, which is more evident for the hollow sample. These unusual anomalies of the longitudinal relaxation rate for T<T$_{B}^{μ+}$ are suggested to be due to the surface spins’ dynamical behavior. Furthermore, for weak applied longitudinal magnetic field (μ$_{0}$H≈15mT) and T<T$_{B}^{μ+}$ we observed damped coherent oscillations of the muon asymmetry, which are a signature of a quasistatic local field at the muon site as probed by muons implanted in the inner magnetic core of the nanoparticles. The muon spin relaxation technique turns out to be very successful to study the magnetic behavior of maghemite nanoparticles and to detect their unusual local spin dynamics in low magnetic field conditions

Controlled Anchoring of Iron-Oxide Nanoparticles on Polymeric Nanofibers: Easy Access to Core@Shell Organic-Inorganic Nanocomposites for Magneto-Scaffolds

Composites combining superparamagnetic iron oxide nanoparticles (SPIONs) and polymers are largely present in modern (bio)materials. However, while SPIONs embedded in polymer matrices are classically reported, the mechanical and degradation properties of the polymer scaffold are impacted by the SPIONs. Therefore, the controlled anchoring of SPIONs onto polymer surfaces is still a major challenge. Herein, we propose an efficient strategy for the direct and uniform anchoring of SPIONs on the surface of functionalized-polylactide (PLA) nanofibers via a simple free ligand exchange procedure to design PLA@SPIONs core@shell nanocomposites. The resulting PLA@SPIONs hybrid biomaterials are characterized by electron microscopy (SEM and TEM) and EDXS analysis, to probe the morphology and detect elements present at the organic/inorganic interface, respectively. A monolayer of SPIONs with a complete and homogeneous coverage is observed on the surface of PLA nanofibers. Magnetization experiments show that magnetic properties of the nanoparticles are well-preserved after their grafting on the PLA fibers and that the size of the nanoparticles does not change. The absence of cytotoxicity, combined with a high sensitivity of detection in MRI both in vitro and in vivo make these hybrid nanocomposites attractive for the development of magnetic biomaterials for biomedical applications

Immobilization of metal hexacyanoferrates in chitin beads for cesium sorption: synthesis and characterization

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Nanosized Heterostructures of Au@Prussian Blue Analogues: Towards Multifunctionality at the Nanoscale

Access to multifunctionality at the nanoscale requires the development of hybrid nanostructures that combine materials of different natures. In this line of thought, current research on coordination polymers is not only focusing on their synthesis at the nanoscale, but also on combining these polymers with other materials. According to a novel and rational approach, single-layer Au@Prussian blue analogue (PBA) and double-layer Au@PBA@PBA′ core–shell nanoparticles (NPs) may be obtained through the growth of a cyano-bridged coordination network on the gold surface. The nanosized heterostructures combine the plasmonic optical properties of the gold core and the magnetic properties of the PBA shell. Whereas the single-layer nanoparticles are paramagnetic, the double-layer nanostructures display ferromagnetism; therefore, the overall structural motif may be considered as multifunctional. The developed synthetic concept also includes an easy access to hollow PBA NPs

Back Cover: Nanosized Heterostructures of Au@Prussian Blue Analogues: Towards Multifunctionality at the Nanoscale

Core–shell gold@Prussian blue analogue nanoparticles that exhibit plasmonic and magnetic properties can be synthesized according to a novel and rational approach that is described by Y. Guari and co-workers in their Communication (DOI: 10.1002/anie.201310443). The developed synthetic concept also includes a smart way to hollow Prussian blue analogue nanoparticles. (Cover artwork: Tania Louis.

Nanosized Heterostructures of Au@Prussian Blue Analogues: Towards Multifunctionality at the Nanoscale

Access to multifunctionality at the nanoscale requires the development of hybrid nanostructures that combine materials of different natures. In this line of thought, current research on coordination polymers is not only focusing on their synthesis at the nanoscale, but also on combining these polymers with other materials. According to a novel and rational approach, single-layer Au@Prussian blue analogue (PBA) and double-layer Au@PBA@PBA′ core–shell nanoparticles (NPs) may be obtained through the growth of a cyano-bridged coordination network on the gold surface. The nanosized heterostructures combine the plasmonic optical properties of the gold core and the magnetic properties of the PBA shell. Whereas the single-layer nanoparticles are paramagnetic, the double-layer nanostructures display ferromagnetism; therefore, the overall structural motif may be considered as multifunctional. The developed synthetic concept also includes an easy access to hollow PBA NPs

Rücktitelbild: Nanosized Heterostructures of Au@Prussian Blue Analogues: Towards Multifunctionality at the Nanoscale

Gold@Preußischblau-Kern@Schale-Nanopartikel mit plasmonischen und magnetischen Eigenschaften wurden mit einer neuen Methode synthetisiert, die von Y. Guari et al. in ihrer Zuschrift (DOI: 10.1002/ange.201310443) beschrieben wird. Auch hohle Preußischblau-Nanopartikel können hergestellt werden. (Titelbild: Tania Louis.