88 research outputs found
Doped-iron oxide nanocrystals synthesized by one-step aqueous route for multi-imaging purposes
New doped inorganic nanocrystals (NC) consisting on iron oxide and other metal integrated into the structure have been synthesized in one-step by adapting the oxidant precipitation synthesis route for magnetite. Different metals have been chosen to confer extra and unique properties to the resulting magnetic hetero-nanostructure: Co and Gd for enhancing transversal and longitudinal relaxivities for magnetic resonance imaging and Bi and Au for achieving X-ray absorption for computed tomography imaging. Apart of that, gold optical properties are interesting for photothermal therapy and iron oxides for magnetic hyperthermia. All metals have been incorporated into the magnetite structure in different ways during the synthesis: by forming a solid solution, by modifying the surface of the NCs, or by co-crystallization with the magnetite. The nanostructure formed in each case depends on the ionic radius of the secondary metal ion and the solubility of its hydroxide that control the co-precipitation in the initial steps of the reaction. Magnetic properties and imaging capabilities of the hetero-nanostructures have been analyzed as a function of the element distribution. Due to the synergistic combination of the different element properties, these magnetic hetero-nanostructures have great potential for biomedical applications
A device-independent approach to evaluate the heating performance during magnetic hyperthermia experiments: peak analysis and zigzag protocol
Accurate knowledge of the heating performance of magnetic nanoparticles
(MNPs) under AC fields is critical for the development of hyperthermia-mediated
applications. Usually reported in terms of the specific loss power (SLP)
obtained from the temperature variation () vs. time (t) curve, such
estimate is subjected to a huge uncertainty. Thus, very different SLP values
are reported for the same particles when measured on different
equipment/laboratories. This lack of control clearly hampers the further
development of MNP-mediated heat-triggered technologies. Here we report a
device-independent approach to calculate the SLP value of a suspension of MNPs:
the SLP is obtained from the analysis of the peak at the field on/off switch of
the curve. The measurement procedure, which itself constitutes a
change of paradigm within the field, is based on fundamental physics
considerations: specifically to guarantee the applicability of Newton's law of
cooling, as i) it corresponds to the ideal scenario in which the temperature
profiles of the system during heating and cooling are the same; and ii) it
diminishes the role of coexistence of various heat dissipation channels. Such
an approach is supported by theoretical and computational calculations to
increase the reliability and reproducibility of SLP determination. This is
experimentally confirmed, demonstrating a reduction in SLP variation across 3
different devices located in 3 different laboratories. Furthermore, the
application of this peak analysis method (PAM) to a rapid succession of field
on/off switches that result in a zigzag-like , which we term the
zigzag protocol, allows evaluating possible variations of the SLP values with
time or temperature.Comment: main text: 30 pages, 9 figure
In-situ particles reorientation during magnetic hyperthermia application: Shape matters twice
Promising advances in nanomedicine such as magnetic hyperthermia rely on a precise control of the nanoparticle performance in the cellular environment. This constitutes a huge research challenge due to difficulties for achieving a remote control within the human body. Here we report on the significant double role of the shape of ellipsoidal magnetic nanoparticles (nanorods) subjected to an external AC magnetic field: first, the heat release is increased due to the additional shape anisotropy; second, the rods dynamically reorientate in the orthogonal direction to the AC field direction. Importantly, the heating performance and the directional orientation occur in synergy and can be easily controlled by changing the AC field treatment duration, thus opening the pathway to combined hyperthermic/ mechanical nanoactuators for biomedicine. Preliminary studies demonstrate the high accumulation of nanorods into HeLa cells whereas viability analysis supports their low toxicity and the absence of apoptotic or necrotic cell death after 24 or 48 h of incubationThis work was partially supported by the EC FP-7 grant “NanoMag” (grant agreement no. 604448), the Spanish Ministry of Economy and Competitiveness (MAT2013-47078-C2-2-P, MAT2014-52069-R, MAT2013-47395-C4-3-R, MAT2015- 67557-C2-1-P-MICINN, CONSOLIDER CSD2007-00041, CTQ2013-48767-C3-3-R), and Gobierno de la Comunidad de Madrid (NANOFRONTMAG, S2013/MIT-2850). D.S. acknowledges financial support from Xunta de Galicia (I2C Postdoctoral Plan). A.T. thanks UAM for a predoctoral contrac
Formation Mechanism of Maghemite Nanoflowers Synthesized by a Polyol-Mediated Process
Magnetic nanoparticles are being
developed as structural and functional
materials for use in diverse areas, including biomedical applications.
Here, we report the synthesis of maghemite (γ-Fe<sub>2</sub>O<sub>3</sub>) nanoparticles with distinct morphologies: single-core
and multicore, including hollow spheres and nanoflowers, prepared
by the polyol process. We have used sodium acetate to control the
nucleation and assembly process to obtain the different particle morphologies.
Moreover, from samples obtained at different time steps during the
synthesis, we have elucidated the formation mechanism of the nanoflowers:
the initial phases of the reaction present a lepidocrocite (γ-FeOOH)
structure, which suffers a fast dehydroxylation, transforming to an
intermediate “undescribed” phase, possibly a partly
dehydroxylated lepidocrocite, which after some incubation time evolves
to maghemite nanoflowers. Once the nanoflowers have been formed, a
crystallization process takes place, where the γ-Fe<sub>2</sub>O<sub>3</sub> crystallites within the nanoflowers grow in size (from
∼11 to 23 nm), but the particle size of the flower remains
essentially unchanged (∼60 nm). Samples with different morphologies
were coated with citric acid and their heating capacity in an alternating
magnetic field was evaluated. We observe that nanoflowers with large
cores (23 nm, controlled by annealing) densely packed (tuned by low
NaAc concentration) offer 5 times enhanced heating capacity compared
to that of the nanoflowers with smaller core sizes (15 nm), 4 times
enhanced heating effect compared to that of the hollow spheres, and
1.5 times enhanced heating effect compared to that of single-core
nanoparticles (36 nm) used in this work
Beyond Newton's law of cooling in evaluating magnetic hyperthermia performance: a device-independent procedure †
Accurate knowledge of the heating performance of magnetic nanoparticles (MNPs) under AC magnetic fields is critical for the development of hyperthermia-mediated applications. Usually reported in terms of the specific loss power (SLP) obtained from the temperature variation (ΔT) vs. time (t) curve, such an estimate is subjected to a huge uncertainty. Thus, very different SLP values are reported for the same particles when measured on different equipment/in different laboratories. This lack of control clearly hampers the further development of nanoparticle-mediated heat-triggered technologies. Here, we report a device-independent approach to calculate the SLP value of a suspension of magnetic nanoparticles: the SLP is obtained from the analysis of the peak at the AC magnetic field on/off switch of the ΔT(time) curve. The measurement procedure, which itself constitutes a change of paradigm within the field, is based on the heat diffusion equation, which is still valid when the assumptions of Newton's law of cooling are not applicable, as (i) it corresponds to the ideal scenario in which the temperature profiles of the system during heating and cooling are the same; and (ii) it diminishes the role of coexistence of various heat dissipation channels. Such an approach is supported by theoretical and computational calculations to increase the reliability and reproducibility of SLP determination. Furthermore, the new methodological approach is experimentally confirmed, by magnetic hyperthermia experiments performed using 3 different devices located in 3 different laboratories. Furthermore, the application of this peak analysis method (PAM) to a rapid succession of stimulus on/off switches which results in a zigzag-like ΔT(t), which we term the zigzag protocol, allows evaluation of possible variations of the SLP values with time or temperature
Whither Magnetic Hyperthermia? A Tentative Roadmap
The scientific community has made great efforts in advancing magnetic hyperthermia for the last two decades after going through a sizeable research lapse from its establishment. All the progress made in various topics ranging from nanoparticle synthesis to biocompatibilization and in vivo testing have been seeking to push the forefront towards some new clinical trials. As many, they did not go at the expected pace. Today, fruitful international cooperation and the wisdom gain after a careful analysis of the lessons learned from seminal clinical trials allow us to have a future with better guarantees for a more definitive takeoff of this genuine nanotherapy against cancer. Deliberately giving prominence to a number of critical aspects, this opinion review offers a blend of state-of-the-art hints and glimpses into the future of the therapy, considering the expected evolution of science and technology behind magnetic hyperthermia
Reversible Alignment of Nanoparticles and Intracellular Vesicles During Magnetic Hyperthermia Experiments
Heating magnetic nanoparticles (MNPs) with AC (Alternating Current) magnetic fields has received significant attention in recent years, particularly for biomedical uses. However, most studies focus on characterizing the heat release, overlooking the fact that the MNPs in the viscous cell environment constitute a dynamic magnetic colloid whose configuration may evolve over time, particularly if a driving force as the AC field is applied. Aiming to shed light on this matter, in this workthe dynamics of the colloid structure during hyperthermia experiments are studied. By combining various experimental and theoretical tools, it is concluded that the AC field may drive the formation of aligned structures, and the impact that such structures may have on the associated heating is assessed. Remarkably, the results show that those field‐driven structures are highly unstable for small particle sizes, rapidly disassembling upon field removal. Moreover, an analogous behavior in vitro is found, with the AC magnetic field also promoting a reversible alignment of vesicles containing the MNPs within the cells. The results suggest that the observed alignment, both of MNPs and intracellular vesicles, may be a common phenomenon in usual hyperthermia experiments, but unnoticed because of the intrinsic unstable nature of the aligned structures
Variable blocking temperature of a porous silicon/Fe3O4 composite due to different interactions of the magnetic nanoparticles
Colloidal Flower-Shaped Iron Oxide Nanoparticles: Synthesis Strategies and Coatings
The assembly of magnetic cores into regular structures may notably influence the properties displayed by a magnetic colloid. Here, key synthesis parameters driving the self-assembly process capable of organizing colloidal magnetic cores into highly regular and reproducible multi-core nanoparticles are determined. In addition, a self-consistent picture that explains the collective magnetic properties exhibited by these complex assemblies is achieved through structural, colloidal, and magnetic means. For this purpose, different strategies to obtain flower-shaped iron oxide assemblies in the size range 25-100 nm are examined. The routes are based on the partial oxidation of Fe(OH)(2), polyol-mediated synthesis or the reduction of iron acetylacetonate. The nanoparticles are functionalized either with dextran, citric acid, or alternatively embedded in polystyrene and their long-term stability is assessed. The core size is measured, calculated, and modeled using both structural and magnetic means, while the Debye model and multi-core extended model are used to study interparticle interactions. This is the first step toward standardized protocols of synthesis and characterization of flower-shaped nanoparticles
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