Gema Martinez

Use of a polyol liquid collection medium to obtain ultrasmall magnetic nanoparticles by laser pyrolysis

The present work addresses the main bottleneck in the synthesis of magnetic nanoparticles by laser pyrolysis. Since the introduction of laser pyrolysis for the production of nanoparticles nearly three decades ago, this method has been repeatedly presented as a highly promising alternative, on account of two main characteristics: (i) its flexibility, since nanoparticles can be formed from a wide variety of precursors in both gas and liquid phase, and (ii) its continuous nature, avoiding the intrinsic variability of batch processing. However, the results reported to date invariably show considerable aggregation of the obtained nanoparticles, which strongly limits their application in most fields. In this work, we have been able to circumvent this problem by collecting the particles in a polyol liquid medium. This method prevents the formation of aggregates and renders a uniform distribution of well dispersed ultrasmall nanoparticles (<4 nm) in a water-compatible solvent. We consider that the effectiveness of this novel collection method for the production of well-dispersed magnetic nanoparticles will be of high interest to a wide range of scientists working in the nanoparticle synthesis field and may enable new applications wherever there is a strict requirement for non-agglomerated nanoparticles.

Porous membranes from acid decorated block copolymer nano-objects via RAFT alcoholic dispersion polymerization

The RAFT dispersion polymerization of methyl methacrylate (MMA) was conducted in ethanol at 70 °C using a poly(methacrylic acid) (PMAA) chain transfer agent. The poly(methacrylic acid) block is soluble in ethanol and acts as a steric stabilizer for the growing insoluble PMMA chains, resulting in the in situ formation of diblock copolymer nano-objects (Polymerization Induced Self-Assembly (PISA)) in the form of spheres, worms or vesicles, depending on the precise reaction conditions as judged by transmission electron microscopy and dynamic light scattering studies. Two detailed phase diagrams using PMAA27 and PMAA47 macro-CTAs were constructed as a road map for the synthesis of pure morphologies. It was observed that the pure phases could be obtained using the longer macro-CTA while the pure worm phase was not observed with the shorter PMAA. Spin-coated thin films of the prepared spherical particles exhibited a connected porous network as evaluated by electron microscopy (SEM, TEM). Finally, the prepared porous thin film was tested as an isoporous membrane for water filtration.

Gold-coated halloysite nanotubes as tunable plasmonic platforms

We propose the use of natural Halloysite Hollow Nanotubes (HNTs) as supports to generate plasmonic platforms with remotely triggered heating capacity. The chemical modification and subsequent coating with nanostructured gold either in the form of individually dispersed particles or by forming a shell with variable thickness and interconnectivity has been studied. The dielectric nature of the silica in conjunction with the plasmonic gold layer allows a flexible optical response with tunable maximum absorptions within the visible to Near-Infrared (NIR) range. The generation of hollow gold nanotubes using halloysite as a sacrificial template is also demonstrated.

Screen-printed nanoparticles as anti-counterfeiting tags

Metallic nanoparticles with different physical properties have been screen printed as authentication tags on different types of paper. Gold and silver nanoparticles show unique optical signatures, including sharp emission bandwidths and long lifetimes of the printed label, even under accelerated weathering conditions. Magnetic nanoparticles show distinct physical signals that depend on the size of the nanoparticle itself. They were also screen printed on different substrates and their magnetic signals read out using a magnetic pattern recognition sensor and a vibrating sample magnetometer. The novelty of our work lies in the demonstration that the combination of nanomaterials with optical and magnetic properties on the same printed support is possible, and the resulting combined signals can be used to obtain a user-configurable label, providing a high degree of security in anti-counterfeiting applications using simple commercially-available sensors.

A Swine Model of Selective Geographic Atrophy of Outer Retinal Layers Mimicking Atrophic AMD: A Phase I Escalating Dose of Subretinal Sodium Iodate

PURPOSE To establish the dose of subretinal sodium iodate (NaIO3) in order to create a toxin-induced large animal model of selective circumscribed atrophy of outer retinal layers, the retinal pigment epithelium (RPE), and photoreceptors, by spectral-domain optical coherence tomography (SD-OCT) and immunocytochemistry. METHODS Fifteen male and female healthy Yorkshire pigs received unilateral subretinal escalating doses of NaIO3 under general anesthesia. In all the animals, volumes of 0.1 to 0.2 mL NaIO3 were injected into the subretinal space of the area centralis through a 23/38-gauge subretinal cannula. Control SD-OCTs were performed 1 and 2 months after the surgery, at which time pigs were euthanized and eyes enucleated. Globes were routinely processed for histologic and immunohistochemical evaluation. RESULTS Spectral-domain OCT and immunohistochemistry revealed circumscribed and well-demarcated funduscopic lesions, limited to the outer retinal layers in pigs treated with 0.01 mg/mL subretinal sodium iodate. CONCLUSIONS The swine model of a controlled area of circumscribed retinal damage, with well-delimited borders, and selectively of the outer layers of the retina presented herein shows several clinical and histologic features of geographic atrophy in AMD. Therefore, it may represent a valuable tool in the investigation of new emerging regenerative therapies that aim to restore visual function, such as stem cell transplantation or optogenetics.

Nano-structured magneto-responsive membranes from block copolymers and iron oxide nanoparticles

Mixed matrix membranes (MMMs) provide an exciting alternative to traditional membranes due to their favorable properties from both building blocks which are essential for certain separation applications. Block copolymer directed synthesis of MMMs is an innovative approach for the preparation of porous materials. In the current work the syntheses of mixed matrix membranes from a PMAA-b-PMMA block copolymer and functionalized iron oxide magnetic nanoparticles are demonstrated. The block copolymers were synthesized using a RAFT polymerization technique, along with three different types of magnetic nanoparticles with various surface properties. The thin film membranes were prepared by mixing different ratios of diblock copolymer in THF and iron oxide nanoparticles in water followed by tape casting or spin coating. The particles and the membranes were characterized using TEM, DLS, and SEM. The permeation behavior of the membranes was assessed using filtration tests in the presence and absence of a magnetic field.

Laser-Assisted Production of Carbon-Encapsulated Pt-Co Alloy Nanoparticles for Preferential Oxidation of Carbon Monoxide

C-encapsulated highly pure PtxCoy alloy nanoparticles have been synthesized by an innovative one-step in-situ laser pyrolysis. The obtained X-ray diffraction pattern and transmission electron microscopy images correspond to PtxCoy alloy nanoparticles with average diameters of 2.4 nm and well-established crystalline structure. The synthesized PtxCoy/C catalyst containing 1.5 wt% of PtxCoy nanoparticles can achieve complete CO conversion in the temperature range 125–175°C working at weight hourly space velocities (WHSV) of 30 L h−1g−1. This study shows the first example of bimetallic nanoalloys synthesized by laser pyrolysis and paves the way for a wide variety of potential applications and metal combinations.

Pumping Metallic Nanoparticles with Spatial Precision within Magnetic Mesoporous Platforms: 3D Characterization and Catalytic Application

The present work shows an efficient strategy to assemble two types of functional nanoparticles onto mesoporous MCM-41 silica nanospheres with a high degree of spatial precision. In a first stage, magnetite nanoparticles are synthesized with a size larger than the support pores and grafted covalently through a peptide-like bonding onto their external surface. This endowed the silica nanoparticles with a strong superparamagnetic response, while preserving the highly ordered interior space for the encapsulation of other functional guest species. Second, we report the finely controlled pumping of preformed Pt nanoparticles (1.5 nm) within the channels of the magnetic MCM-41 nanospheres to confer an additional catalytic functionality to the multiassembled nanoplatform. The penetration depth of the metallic nanoparticles can be explained as a result of the interplay between the particle-wall electrostatic attraction and the repulsive forces between neighboring Pt nanoparticles. A detailed transmission electron microscopy and a 3D high-resolution high-angle annular dark-field detector electron tomography study were carried out to characterize the material and to explain the assembly mechanism. Finally, the performance of these multifunctional nanohybrids as magnetically recoverable catalysts has been evaluated in the selective hydrogenation of p-nitrophenol, a well-known pollutant and intermediate in multiple industrial processes.