C. Marquina

Nanoparticle penetration and transport in living pumpkin plants: in situ subcellular identification

BackgroundIn recent years, the application of nanotechnology in several fields of bioscience and biomedicine has been studied. The use of nanoparticles for the targeted delivery of substances has been given special attention and is of particular interest in the treatment of plant diseases. In this work both the penetration and the movement of iron-carbon nanoparticles in plant cells have been analyzed in living plants of Cucurbita pepo.ResultsThe nanoparticles were applied in planta using two different application methods, injection and spraying, and magnets were used to retain the particles in movement in specific areas of the plant. The main experimental approach, using correlative light and electron microscopy provided evidence of intracellular localization of nanoparticles and their displacement from the application point. Long range movement of the particles through the plant body was also detected, particles having been found near the magnets used to immobilize and concentrate them. Furthermore, cell response to the nanoparticle presence was detected.ConclusionNanoparticles were capable of penetrating living plant tissues and migrating to different regions of the plant, although movements over short distances seemed to be favoured. These findings show that the use of carbon coated magnetic particles for directed delivery of substances into plant cells is a feasible application.

Magnetic nanoparticles for power absorption: Optimizing size, shape and magnetic properties

We present a study on the magnetic properties of naked and silica-coated Fe{sub 3}O{sub 4} nanoparticles with sizes between 5 and 110 nm. Their efficiency as heating agents was assessed through specific power absorption (SPA) measurements as a function of particle size and shape. The results show a strong dependence of the SPA with the particle size, with a maximum around 30 nm, as expected for a Neel relaxation mechanism in single-domain particles. The SiO{sub 2} shell thickness was found to play an important role in the SPA mechanism by hindering the heat outflow, thus decreasing the heating efficiency. It is concluded that a compromise between good heating efficiency and surface functionality for biomedical purposes can be attained by making the SiO{sub 2} functional coating as thin as possible. - Graphical Abstract: The magnetic properties of Fe{sub 3}O{sub 4} nanoparticles from 5 to 110 nm are presented, and their efficiency as heating agents discussed as a function of particle size, shape and surface functionalization.

A systematic study of structural, magnetic and electrical properties of perovskites

A thorough study of the series has been carried out. All of the samples have the same orthorhombic crystallographic structure. However, the magnetic, magnetoelastic and electrical properties show drastic changes with the Tb content. The decrease in the intensity of the ferromagnetic double-exchange interaction has been correlated with the increase in the Tb content and the decrease in the Mn - O - Mn bond angle, which leads to a decrease in the electron transfer between Mn 3d and O 2p orbitals. Two magnetic phases have been detected at low temperatures: an insulator spin-glass phase in samples with high Tb contents and a metallic ferromagnetic phase in samples with low Tb contents.

Absorption and translocation to the aerial part of magnetic carbon-coated nanoparticles through the root of different crop plants

The development of nanodevices for agriculture and plant research will allow several new applications, ranging from treatments with agrochemicals to delivery of nucleic acids for genetic transformation. But a long way for research is still in front of us until such nanodevices could be widely used. Their behaviour inside the plants is not yet well known and the putative toxic effects for both, the plants directly exposed and/or the animals and humans, if the nanodevices reach the food chain, remain uncertain. In this work we show that magnetic carbon-coated nanoparticles forming a biocompatible magnetic fluid (bioferrofluid) can easily penetrate through the root in four different crop plants (pea, sunflower, tomato and wheat). They reach the vascular cylinder, move using the transpiration stream in the xylem vessels and spread through the aerial part of the plants in less than 24 hours. Accumulation of nanoparticles was detected in wheat leaf trichomes, suggesting a way for excretion/detoxification. This kind of studies is of great interest in order to unveil the movement and accumulation of nanoparticles in plant tissues for assessing further applications in the field or laboratory.

Highly magnetic silica-coated iron nanoparticles prepared by the arc-discharge method

In spite of encouraging progress in recent years, the development of magnetic nanoparticles that can be used as drug delivery vectors remains a significant challenge for materials scientists. Among the multiple hurdles that must be overcome are the provision of a sufficiently high magnetic response, a high loading capacity for therapeutic or diagnosis materials and a sufficient degree of biocompatibility. In this work we describe the preparation of encapsulated magnetic nanoparticles consisting of a metallic iron core and an amorphous silica shell by using a modification of the arc-discharge method. This is a simple and inexpensive way to produce well-coated iron nanoparticles. The particles thus obtained present a much stronger magnetic response than any composite material produced up to now involving magnetic nanoparticles encapsulated in inorganic matrices, and the rich chemistry and easy functionalization of the silica outer surface make them promising materials for their application as magnetic carriers.

Magnetic nanoparticles for local drug delivery using magnetic implants

Magnetic nanoparticles are good candidates used for the targeted delivery of anti-tumor agents. They can be concentrated on a desired region, reducing collateral effects and improving the efficiency of the chemotherapy. We propose a method in which permanent magnets are implanted by laparoscopic technique directly in the affected organ. This method proposes the use of Fe@C nanoparticles, which are loaded with doxorubicin and injected intravenously. The particles, once attracted to the magnet, release the drug at the tumor region. This method seems to be more promising and effective than that based on the application of external magnetic fields.

Giant room‐temperature magnetoresistance in the FeRh alloy

The magnetoresistance of the FeRh alloy has been measured in the temperature range 200–300 K using high pulsed magnetic fields up to 36 T. This compound shows a first‐order magnetic transition from the antiferromagnetic (AF) low‐temperature state to the ferromagnetic (F) high‐temperature state at TAF–F=405 K. The F state is very close in energy to the AF state and can be reached by applying a magnetic field. The measurements made within the AF state show that the AF–F transition is accompanied by a giant magnetoresistance effect (ΔR/R≊50%).

Cell death induced by the application of alternating magnetic fields to nanoparticle-loaded dendritic cells

In this work, the capability of primary, monocyte-derived dendritic cells (DCs) to uptake iron oxide magnetic nanoparticles (MNPs) is assessed and a strategy to induce selective cell death in these MNP-loaded DCs using external alternating magnetic fields (AMFs) is reported. No significant decrease in the cell viability of MNP-loaded DCs, compared to the control samples, was observed after five days of culture. The number of MNPs incorporated into the cytoplasm was measured by magnetometry, which confirmed that 1-5 pg of the particles were uploaded per cell. The intracellular distribution of these MNPs, assessed by transmission electron microscopy, was found to be primarily inside the endosomic structures. These cells were then subjected to an AMF for 30 min and the viability of the blank DCs (i.e. without MNPs), which were used as control samples, remained essentially unaffected. However, a remarkable decrease of viability from approximately 90% to 2-5% of DCs previously loaded with MNPs was observed after the same 30 min exposure to an AMF. The same results were obtained using MNPs having either positive (NH(2)(+)) or negative (COOH(-)) surface functional groups. In spite of the massive cell death induced by application of AMF to MNP-loaded DCs, the number of incorporated magnetic particles did not raise the temperature of the cell culture. Clear morphological changes at the cell structure after magnetic field application were observed using scanning electron microscopy. Therefore, local damage produced by the MNPs could be the main mechanism for the selective cell death of MNP-loaded DCs under an AMF. Based on the ability of these cells to evade the reticuloendothelial system, these complexes combined with an AMF should be considered as a potentially powerful tool for tumour therapy.

Effect of Mn substitution on the volume and magnetic properties of Er2Fe17

The effects of Mn substitution on the magnetic properties of Er2Fe17−xMnx compounds have been investigated by different experimental techniques. An unusual composition dependence of the unit cell volume at room temperature occurs due to a strong magnetovolume effect, which has been confirmed by high temperature linear thermal expansion measurements. From magnetization measurements the composition dependence of the spontaneous magnetization of the 3d-sublattice magnetic moment and of the Curie temperature has been determined. Spin reorientation has been detected for compounds with 3⩽x⩽5.5, as well as remarkable magnetic history effects.

Magnetic properties and energy absorption of CoFe2O4 nanoparticles for magnetic hyperthermia

We have studied the magnetic and power absorption properties of three samples of CoFe2O4 nanoparticles with sizes from 5 to 12 nm prepared by thermal decomposition of Fe (acac)3 and Co(acac)2 at high temperatures. The blocking temperatures TB estimated from magnetization M(T) curves spanned the range 180 ≤ T B ≤ 320 K, reflecting the large magnetocrystalline anisotropy of these nanoparticles. Accordingly, high coercive fields HC ≈ 1.4 - 1.7 T were observed at low temperatures. Specific Power Absorption (SPA) experiments carried out in ac magnetic fields indicated that, besides particle volume, the effective magnetic anisotropy is a key parameter determining the absorption efficiency. SPA values as high as 98 W/g were obtained for nanoparticles with average size of ≈ 12 nm.