Eduardo Ortega

Silica nanoparticles induce cardiotoxicity interfering with energetic status and Ca2+ handling in adult rat cardiomyocytes

Recent evidence has shown that nanoparticles that have been used to improve or create new functional properties for common products may pose potential risks to human health. Silicon dioxide (SiO2) has emerged as a promising therapy vector for the heart. However, its potential toxicity and mechanisms of damage remain poorly understood. This study provides the first exploration of SiO2-induced toxicity in cultured cardiomyocytes exposed to 7- or 670-nm SiO2 particles. We evaluated the mechanism of cell death in isolated adult cardiomyocytes exposed to 24-h incubation. The SiO2 cell membrane association and internalization were analyzed. SiO2 showed a dose-dependent cytotoxic effect with a half-maximal inhibitory concentration for the 7 nm (99.5 ± 12.4 µg/ml) and 670 nm (>1,500 µg/ml) particles, which indicates size-dependent toxicity. We evaluated cardiomyocyte shortening and intracellular Ca2+ handling, which showed impaired contractility and intracellular Ca2+ transient amplitude during β-adrenergic stimulation in SiO2 treatment. The time to 50% Ca2+ decay increased 39%, and the Ca2+ spark frequency and amplitude decreased by 35 and 21%, respectively, which suggest a reduction in sarcoplasmic reticulum Ca2+-ATPase (SERCA) activity. Moreover, SiO2 treatment depolarized the mitochondrial membrane potential and decreased ATP production by 55%. Notable glutathione depletion and H2O2 generation were also observed. These data indicate that SiO2 increases oxidative stress, which leads to mitochondrial dysfunction and low energy status; these underlie reduced SERCA activity, shortened Ca2+ release, and reduced cell shortening. This mechanism of SiO2 cardiotoxicity potentially plays an important role in the pathophysiology mechanism of heart failure, arrhythmias, and sudden death.NEW & NOTEWORTHY Silica particles are used as novel nanotechnology-based vehicles for diagnostics and therapeutics for the heart. However, their potential hazardous effects remain unknown. Here, the cardiotoxicity of silica nanoparticles in rat myocytes has been described for the first time, showing an impairment of mitochondrial function that interfered directly with Ca2+ handling.

Complex Three-Dimensional Magnetic Ordering in Segmented Nanowire Arrays

A comprehensive three-dimensional picture of magnetic ordering in high-density arrays of segmented FeGa/Cu nanowires is experimentally realized through the application of polarized small-angle neutron scattering. The competing energetics of dipolar interactions, shape anisotropy, and Zeeman energy in concert stabilize a highly tunable spin structure that depends heavily on the applied field and sample geometry. Consequently, we observe ferromagnetic and antiferromagnetic interactions both among wires and between segments within individual wires. The resulting magnetic structure for our nanowire sample in a low field is a fan with magnetization perpendicular to the wire axis that aligns nearly antiparallel from one segment to the next along the wire axis. Additionally, while the low-field interwire coupling is ferromagnetic, application of a field tips the moments toward the nanowire axis, resulting in highly frustrated antiferromagnetic stripe patterns in the hexagonal nanowire lattice. Theoretical calculations confirm these observations, providing insight into the competing interactions and resulting stability windows for a variety of ordered magnetic structures. These results provide a roadmap for designing high-density magnetic nanowire arrays for spintronic device applications.

Core-shell magnetoelectric nanorobot – A remotely controlled probe for targeted cell manipulation

We have developed a remotely controlled dynamic process of manipulating targeted biological live cells using fabricated core-shell nanocomposites, which comprises of single crystalline ferromagnetic cores (CoFe2O4) coated with crystalline ferroelectric thin film shells (BaTiO3). We demonstrate them as a unique family of inorganic magnetoelectric nanorobots (MENRs), controlled remotely by applied a.c. or d.c. magnetic fields, to perform cell targeting, permeation, and transport. Under a.c. magnetic field excitation (50 Oe, 60 Hz), the MENR acts as a localized electric periodic pulse generator and can permeate a series of misaligned cells, while aligning them to an equipotential mono-array by inducing inter-cellular signaling. Under a.c. magnetic field (40 Oe, 30 Hz) excitation, MENRs can be dynamically driven to a targeted cell, avoiding untargeted cells in the path, irrespective of cell density. D.C. magnetic field (−50 Oe) excitation causes the MENRs to act as thrust generator and exerts motion in a group of cells.

Magnetic ordering in 45 nm-diameter multisegmented FeGa/Cu nanowires: single nanowires and arrays

Magnetic nanowires are ideal candidates for many diverse applications, such as 3D magnetic memory and bio-barcodes, they also allow fundamental studies of magnetic interactions at the nanometer level. Usually their magnetic characterization involves hysteresis loops that represent the weighted averages of each entire array. Here, off-axis electron holography under Lorentz microscopy conditions has been used to observe the magnetization distribution and to determine the saturation magnetization (Ms = 1.26 × 106 A m−1) of a single 45 nm diameter FeGa(10.5 nm)/Cu(6.5 nm) nanowire. In addition, a row of segmented nanowires still within the alumina growth template was carefully sliced from the array to observe the magnetization distribution resulting from interwire as well as intersegment interactions. Two simultaneous magnetic states were observed in this novel experimental configuration: one is the antiferromagnetic ordering of segments along each wire with ferromagnetic ordering between nanowires and the second is the presence of ferromagnetic vortices along nanowire lengths. Simulations have been performed to verify the presence of both remnant states. These states demonstrate the frustration present in hexagonally packed nanowires and demonstrate the necessity to understand long range magnetic ordering for applications such as 3D magnetic memory.

In-situ magnetization/heating electron holography to study the magnetic ordering in arrays of nickel metallic nanowires

Magnetic nanostructures of different size, shape, and composition possess a great potential to improve current technologies like data storage and electromagnetic sensing. In thin ferromagnetic nanowires, their magnetization behavior is dominated by the competition between magnetocrystalline anisotropy (related to the crystalline structure) and shape anisotropy. In this way electron diffraction methods like precession electron diffraction (PED) can be used to link the magnetic behavior observed by Electron Holography (EH) with its crystallinity. Using off-axis electron holography under Lorentz conditions, we can experimentally determine the magnetization distribution over neighboring nanostructures and their diamagnetic matrix. In the case of a single row of nickel nanowires within the alumina template, the thin TEM samples showed a dominant antiferromagnetic arrangement demonstrating long-range magnetostatic interactions playing a major role.

Phase Identification of III-N Thin Films Grown by Molecular Beam Epitaxy and Migration Enhanced Epitaxy using Precession Electron Diffraction

Group III nitrides are semiconductor materials with a wide application in electronic and optoelectronic devices. The study of these materials has been carried out using mainly the stable phase, which has a hexagonal (wurtzite) structure. However, this crystal phase presents large spontaneous and piezoelectric polarization fields that limit the free-carrier recombination efficiency. Recently, in order to avoid the intrinsic polarization fields in electronic devices, intensive efforts have been made to grow the group III nitrides in the metastable phase, which has a cubic (zinc blende) structure. One of the most important compound for III’N thin films is Gallium Nitride (GaN), this material together with its alloys are suitable for developing photovoltaic and optolectronic applicatins with a high efficiency. This is mainly due their direct energy gap, that covers a large part of the solar spectrum, from infrared with InN to the ultraviolet with GaN and AlN. Another important compound for III-N thin films is Indium Nitride (InN) which has the highest electronic mobility, the best doping properties, the lowest phonon scattering, and smallest direct band gap among the III-N family [1,2]. However, nowadays a higher crystalline quality and smaller hexagonal inclusion in c-InN samples are still challenging due to a low dissociation temperature of the compound and the metastability of the cubic phase due lattice mismatch.

Morphology visualization of irregular shape bacteria by electron holography and tomography

In the current work, irregular morphology of Staphylococcus aureus bacteria has been visualized by phase retrieval employing off‐axis electron holography (EH) and 3D reconstruction electron tomography using high‐angle annular dark field scanning transmission electron microscopy (HAADF‐STEM). Bacteria interacting with gold nanoparticles (AuNP) acquired a shrunken or irregular shape due to air dehydration processing. STEM imaging shows the attachment of AuNP on the surface of cells and suggests an irregular 3D morphology of the specimen. The phase reconstruction demonstrates that off‐axis electron holography can reveal with a single hologram the morphology of the specimen and the distribution of the functionalized AuNPs. In addition, EH reduces significantly the acquisition time and the cumulative radiation damage (in three orders of magnitude) over biological samples in comparison with multiple tilted electron expositions intrinsic to electron tomography, as well as the processing time and the reconstruction artifacts that may arise during tomogram reconstruction.

Structural damage reduction in protected gold clusters by electron diffraction methods

The present work explores electron diffraction methods for studying the structure of metallic clusters stabilized with thiol groups, which are susceptible to structural damage caused by electron beam irradiation. There is a compromise between the electron dose used and the size of the clusters since they have small interaction volume with electrons and as a consequence weak reflections in the diffraction patterns. The common approach of recording individual clusters using nanobeam diffraction has the problem of an increased current density. Dosage can be reduced with the use of a smaller condenser aperture and a higher condenser lens excitation, but even with those set ups collection times tend to be high. For that reason, the methods reported herein collects in a faster way diffraction patterns through the scanning across the clusters under nanobeam diffraction mode. In this way, we are able to collect a map of diffraction patterns, in areas with dispersed clusters, with short exposure times (milliseconds) using a high sensitive CMOS camera. When these maps are compared with their theoretical counterparts, oscillations of the clusters can be observed. The stability of the patterns acquired demonstrates that our methods provide a systematic and precise way to unveil the structure of atomic clusters without extensive detrimental damage of their crystallinity.

Controlled Magnetization by Electron Holography of Polycrystalline Cobalt Nanowires

Nowadays the comprehensive understanding of nanoscale materials and their physical properties are of great interest to the scientific and technological community. In particular, magnetic nanostructures of different size, shape and composition (e.g. nanoparticles, nanowires or thin films) possess a great potential to improve current technologies in areas such as: magnetic data storage, electromagnetic sensing [1-2]. Lately, soft magnetic nanowires, (Co, Fe & Ni) have been studied for a while experimentally and by simulations, but there still some questions to be address. Soft magnetic nanowires can switch magnetization in two different modes depending on their thickness, these modes are known as the transverse wall mode and the vortex wall mode. In thin ferromagnetic nanowires (diameter less than 40nm) a simple domain wall nucleates and propagates along the nanowire axis, while the reversal of thick nanowires (diameter more than 40 nm) is achieved via localized curling or vortex mode. The magnetization direction of each magnetic domain will be influenced by the magnetocrystalline anisotropy; typically following the easy magnetization axis, which minimize the magnetocrystalline energy. The magnetization behavior in this nanostructures is dominated by the competition between magnetocrystalline anisotropy and shape anisotropy. In many cases this competition between can frustrates the magnetization direction. It is expected that the magnetostatic coupling between nanostructures have a strong influence on their response to an external field [3].