Verónica Salgueiriño

Hollow‐Shelled Nanoreactors Endowed with High Catalytic Activity

Hollow-shelled nanoreactors have emerged as efficient structures to maximize the potential of nanoparticles in the field of catalysis. In this Concept article, we underline the importance of both the morphology of the active nanoparticles as well as the composition and porosity of the shell for the catalytic performance of the overall nanocomposite. Different configurations are discussed, with a focus on preparative methods and applications in organic synthesis. Perspectives on future designs that may offer new opportunities to improve the selectivity of the catalyzed transformations and add additional features are also addressed, in order to illustrate the potential of these unique nanostructures.

Highly Active Nanoreactors: Nanomaterial Encapsulation Based on Confined Catalysis**

It happens inside: highly active nanoreactors are prepared by encapsulating dendritic Pt nanoparticles (NPs) grown on a polystyrene template inside hollow porous silica capsules. The catalytic activity of these Pt NPs is preserved after encapsulation and template removal. Different metals, such as Ni, can thus be reduced inside the capsules, thereby leading to the formation of composites with tunable magnetic properties.

Room-Temperature Ferromagnetism in Antiferromagnetic Cobalt Oxide Nanooctahedra

Cobalt oxide octahedra were synthesized by thermal decomposition. Each octahedron-shaped nanoparticle consists of an antiferromagnetic CoO core enclosed by eight {111} facets interfaced to a thin (∼ 4 nm) surface layer of strained Co3O4. The nearly perfectly octahedral shaped particles with 20, 40, and 85 nm edge length show a weak room-temperature ferromagnetism that can be attributed to ferromagnetic correlations appearing due to strained lattice configurations at the CoO/Co3O4 interface.

Magnetic silica nanoparticle cellular uptake and cytotoxicity regulated by electrostatic polyelectrolytes-DNA loading at their surface.

Magnetic silica nanoparticles show great promise for drug delivery. The major advantages correspond to their magnetic nature and ease of biofunctionalization, which favors their ability to interact with cells and tissues. We have prepared magnetic silica nanoparticles with DNA fragments attached on their previously polyelectrolyte-primed surface. The remarkable feature of these materials is the compromise between the positive charges of the polyelectrolytes and the negative charges of the DNA. This dual-agent formulation dramatically changes the overall cytotoxicity and chemical degradation of the nanoparticles, revealing the key role that surface functionalization plays in regulating the mechanisms involved.

Tailoring the magnetic properties of nickel nanoshells through controlled chemical growth

A wet-chemistry-based synthetic method has been devised for the preparation of core–shell particles with tunable magnetic properties. Tailoring was achieved through variations in the amount of magnetic material deposited. The fabrication of these superparamagnetic particles (with TB below or above room temperature), consequently permits us to envisage different applications, overcoming well-known drawbacks such as the superparamagnetic limit at room temperature.

Double-Fueled Janus Swimmers with Magnetotactic Behavior

Self-propelled particles attract a great deal of attention due to the auspicious range of applications for which nanobots can be used. In a biomedical context, self-propelled swimmers hold promise to autonomously navigate to a desired location in an attempt to counteract cell/tissue defects either by releasing drugs or by performing surgical tasks. The vast majority of prior reports deal with single engine assemblies, often utilizing fuel molecules which are considered to be highly cytotoxic. Herein, we introduce two engines: (1) a motor which couples enzymes (i.e., glucose oxidase) and inorganic nanoparticles (i.e., platinum nanoparticles) to gain power and (2) a peptide-fueled trypsin motor. We demonstrate that both engines can induce enhanced diffusion properties of (Janus) particles using bioavailable and completely harmless fuel molecules. By combining both engines on the same carrier, we show self-propelled particles employing two independent engines, using two different fuels. A collaborative enhancement of the swimmers diffusion properties upon powering-up both engines simultaneously is observed. Additionally, the incorporation of magnetic nanoparticles allows for the swimmer to move in a magnetic gradient upon applying an external magnetic field, yielding in directional motion of the double-fueled particles. These multiple-fueled biocompatible swimmers are a significant contribution to make them applicable in a biomedical context.

Electrostatic doping as a source for robust ferromagnetism at the interface between antiferromagnetic cobalt oxides

Polar oxide interfaces are an important focus of research due to their novel functionality which is not available in the bulk constituents. So far, research has focused mainly on heterointerfaces derived from the perovskite structure. It is important to extend our understanding of electronic reconstruction phenomena to a broader class of materials and structure types. Here we report from high-resolution transmission electron microscopy and quantitative magnetometry a robust – above room temperature (Curie temperature TC ≫ 300 K) – environmentally stable- ferromagnetically coupled interface layer between the antiferromagnetic rocksalt CoO core and a 2–4 nm thick antiferromagnetic spinel Co3O4 surface layer in octahedron-shaped nanocrystals. Density functional theory calculations with an on-site Coulomb repulsion parameter identify the origin of the experimentally observed ferromagnetic phase as a charge transfer process (partial reduction) of Co3+ to Co2+ at the CoO/Co3O4 interface, with Co2+ being in the low spin state, unlike the high spin state of its counterpart in CoO. This finding may serve as a guideline for designing new functional nanomagnets based on oxidation resistant antiferromagnetic transition metal oxides.

Synergy effects of magnetic silica nanostructures for drug delivery applications

This article presents a capable strategy of using hybrid nanostructures to improve the magnetic-based performance jointly with the internalization process into cells, for drug delivery applications. The promising combination stems from the concept of magnetic silica nanostructures, referring to magnetic nanoparticles of transition metal ferrites, coated with a silica (or hydroxyapatite) shell or included in a hollow silica nanostructure, such that they can offer a proper and controlled drug delivery. The synergy effects are brought on considering several characteristics; the magnetic properties of the transition metal ferrites as aggregates, the increased biocompatibility, the reduced toxicity, the porosity, the suitable chemical functionalization of silica and different effects such as local heating based on hyperthermia or other triggering effects for a time-space controlled drug delivery.

Assessment of DNA complexation onto polyelectrolyte-coated magnetic silica nanoparticles

The polyelectrolyte-DNA complexation method to form magnetoplexes using silica-coated iron oxide magnetic nanoparticles as inorganic substrates is an attractive and promising process in view of the potential applications including magnetofection, DNA extraction and purification, and directed assembly of nanostructures. Herein, we present a systematic physico-chemical study that provides clear evidence of the type of interactions established, reflects the importance of the DNA length, the nanoparticle size and the ionic strength, and permits the identification of the parameters controlling both the stability and the type of magnetoplexes formed. This information can be used to develop targeted systems with properties optimized for the various proposed applications of magnetoplexes.

Ostwald ripening of platinum nanoparticles confined in a carbon nanotube/silica-templated cylindrical space

Sintering of nanoparticles mediated by an Ostwald ripening mechanism is generally assessed examining the final particle size distributions. Based on this methodology, a general approach for depositing platinum nanoparticles onto carbon nanotubes in solution has been employed in order to evaluate the sintering process of these metallic nanoparticles at increasing temperatures in a carbon nanotube/silica-templated confined space.