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Magnetic heating, namely, the use of heat released by magnetic nanoparticles (MNPs) excited with a high-frequency magnetic field, has so far been mainly used for biological applications. More recently, it has been shown that this heat can be used to catalyze chemical reactions, some of them occurring at temperatures up to 700 °C. The full exploitation of MNP heating properties requires the knowledge of the temperature dependence of their heating power up to high temperatures. Here, a setup to perform such measurements is described based on the use of a pyrometer for high-temperature measurements and on a protocol based on the acquisition of cooling curves, which allows us to take into account calorimeter losses. We demonstrate that the setup permits to perform measurements under a controlled atmosphere on solid state samples up to 550 °C. It should in principle be able to perform measurements up to 900 °C. The method, uncertainties, and possible artifacts are described and analyzed in detail. The influence on losses of putting under vacuum different parts of the calorimeter is measured. To illustrate the setup possibilities, the temperature dependence of heating power is measured on four samples displaying very different behaviors. Their heating power increases or decreases with temperature, displaying temperature sensibilities ranging from -2.5 to +4.4% K-1. This setup is useful to characterize the MNPs for magnetically heated catalysis applications and to produce data that will be used to test models permitting to predict the temperature dependence of MNP heating power.

Magnetic hyperthemia has already been approved for therapy of cancer and other diseases. The treatment involves a direct injection of nanoparticles into the tumor and the application of an alternating magnetic field until temperature at the borders of the tumor is reaching 43 °C. As the heating power of magnetic nanoparticles is moderate, the amount nanoparticles to be injected for this purpose is very high and that means a long process until the nanoparticles are cleared from the body. On the other hand cell experiments indicate that cell dead can be produced without are increase of the cell temperature. This is suggesting that the development of local intracellular hyperthermia involving a smaller number of particles would be very possible. In order to make this strategy effective an adequate monitoring of the nanoheaters local temperature will be required. In order to investigate this pint we have developed a magnetic nanoplafform that incorporates a luminescent molecular thermometer. The thermometer is based on the luminescence emission of two lanthanide complexes with organic ligands that are located on the surface of the magnetic nucleus and in the interior of the hydrophobic part of an amphiphilic copolymer. One of the lanthanides emits with a constant intensity while the intensity of emission of the other decreases with the temperature, thus the ratio of emission intensities gives the absolute temperature on the surface of the nanoparticle beater. The thermometer shows a line sensitive (5.8%K at 296 K), low uncertainly (0.5K), high reproducibility (>99.5%), and fast time magnetic field reveal the existence of an important temperature gradient between nanoheaters and irreversible intracellular damage in tumor cells leading to cell death without having to increase the temperature of the whole tumor mass. A proof of concept of temperature mapping has been realized on cells that were incubated with the nanoparticles.

Iron oxide nanoparticles have found an increasing number of biomedical applications as sensing or trapping platforms and therapeutic and/or diagnostic agents. Most of these applications are based on their magnetic properties, which may vary depending on the nanoparticle aggregation state and/or concentration. In this work, we assess the effect of the inter- and intra-aggregate magnetic dipolar interactions on the heat dissipation power and AC hysteresis loops upon increasing the nanoparticle concentration and the hydrodynamic aggregate size. We observe different effects produced by inter- (long distance) and intra-aggregate (short distance) interactions, resulting in magnetizing and demagnetizing effects, respectively. Consequently, the heat dissipation power under alternating magnetic fields strongly reflects such different interacting phenomena. The intra-aggregate interaction results were successfully modeled by numerical simulations. A better understanding of magnetic dipolar interactions is mandatory for achieving a reliable magnetic hyperthermia response when nanoparticles are located into biological matrices.

As nanotechnology progresses, new demands and new challenges arise. lndeed, the increased interest on hyperthermia therapies in nanomedicine has opened the need for an accurate control of heat transfer and heat release by a precise monitoring of the temperature. A straightforward solution to this demand would be the development of efficient and sensitive nanoparticles embedding both heaters and thermometers, something that despite intense activity in the recent years had resisted scientific efforts. Here we report the development of such device: a nanoplatforrn consisting in a magnetic nanoparticle incorporating a molecular thermometer just on the surface of the heater, thus having an unprecedented thermal contact and a quasi-instantaneous onset of temperature gradient from the heater to the medium. The heater/thermometer nanoplatform was prepared from iron oxide cores functionalized with Eu3+ and Tb3+ complexes, coated with a P4VP-b-P(PMEGAco-PEGA) copolymer and dispersed in water to obtain an aqueous ferrofluid suspension. The thermometric response results from thermally activated energy transfer between Eu3+- and Tb3+-emitting levels and triplet energy states of the ligands and of the host matrix. The beads thermometric performance is evaluated using the relative sensitivity Sr= (::/T)/:: which ranges from 0.5 to 5.8%/K, 295-315 K (maximum sensitivity of 5.8%/K at 296 K). Upon 10 consecutive temperature cycles between 297 and 310 K, the therrnometer reproducibility is 99.5%,. The time fluctuations of the therrnometric parameter :: are always below O. 7%. The uncertainty of the temperature measurement is 0.5 K. The heater/thermometer nanoplatforrn is applied to monitor local temperature changes under ac magnetic fields. A semiconductor thermometer immersed in the ferrofluid and an infrared camera focused on the container wall were used for comparative purposes. A multiple-pulse protocol is illustrated in the Figure showing differences between the fast and direct t

Whereas efficient and sensitive nanoheaters and nanothermometers are demanding tools in modern bio- and nanomedicine, joining both features in a single nanoparticle still remains a real challenge, despite the recent progress achieved, most of it within the last year. Here we demonstrate a successful realization of this challenge. The heating is magnetically induced, the temperature readout is optical, and the ratiometric thermometric probes are dual-emissive Eu3+/Tb3+ lanthanide complexes. The low thermometer heat capacitance (0.021·K-1) and heater/thermometer resistance (1 K·W-1), the high temperature sensitivity (5.8%·K-1 at 296 K) and uncertainty (0.5 K), the physiological working temperature range (295-315 K), the readout reproducibility (>99.5%), and the fast time response (0.250 s) make the heater/thermometer nanoplatform proposed here unique. Cells were incubated with the nanoparticles, and fluorescence microscopy permits the mapping of the intracellular local temperature using the pixel-by-pixel ratio of the Eu3+/Tb3+ intensities. Time-resolved thermometry under an ac magnetic field evidences the failure of using macroscopic thermal parameters to describe heat diffusion at the nanoscale.

Biomedical applications of superparamagnetic iron oxide particles have been of interest for quite a number of years. Recent developments show that multifunctionality can be efficiently achieved using polymers to coat the particles and to provide anchoring elements to their surface. This leads to the formation of nanobeads with a reduced number of particles trapped by the polymeric structure. While the magnetothermic behavior of isolated nanoparticles has been a subject of interest over the past several years, multicore magnetic nanobeads have thus far not received the same attention. The influence of structural and magnetic properties in the hyperthermia performance of a series of magnetic fluids designed for biomedical purposes is studied here. The fluids are made of maghemite multicore polymeric beads, with variable nanoparticle size and hydrodynamic size, dispersed in a buffer solution. The specific loss power (SLP) was measured from 5 to 100 kHz with a field intensity of 21.8 kA/m. SLP increases with increasing magnetic core size, reaching 32 W/g Fe 2O3 at 100 kHz for 16.2 nm. Within the framework of the linear response theory, a graphical construction is proposed to describe the interplay of both size distributions and magnetic properties in the heating performance of such fluids in a given frequency range. Furthermore, a numerical model is developed to calculate the spare contribution of Néel and Brown relaxation mechanisms to SLP, which gives a fair reproduction of the experimental data. © 2013 American Physical Society.

Working machinery in life is nanometric, thus, it is no wonder tliat the development of adequate nanotools would be very helpful in biomedical science. In this direction, the idea behind this work is to build a nanoplatform that can incorporate, in an easy way, multiple physical and biological functionalities. The core of the platform is an hydrophobic polymer that may be used as a matrix for the encapsulation of inorganic nanoparticles (magnetic, luminescent, radioactive, . . .). This matrix contains a Michael acceptor (or an acceptor) on its surface for functionalization. Organic bioactive molecules are attached to one end of a hydrophilic polymer (Le. PEG) terminated on a Michael acceptor (or a donor), and then they are anchored to the hydrophobic core by Michael addition. This system has the advantages of a clean synthesis (no by-products), mild conditions, and an easy and controlled multifunctionalization. The nanoplatform has been functionalized with radiochemical tracers (In111), luminescent dyes (fluorescein, rhodamine, lanthanide compounds), and magnetic nanoparticles, and therefore it can be a powerful tool in imaging. Besides, it has also been functionalized with a therapeutical drug, an antibody, and an optical thermometer made of lanthanide complexes. Health safety of tlhe system has been tested in cellular and in vivo assays. The nanoplatform is highly stable in biological fluids, shows low cell toxicity, high capacity of cell internalization, excellent hematocompatibility, and anticoagulation properties. It is shown that magnetic properties can be tuned up in the whole superparamagnetic range. Moreover, the system has shown excellent performance in magnetic resonance imaging and liyperthermia.

We report on the fabrication of nanocontacts by indentation of an ultrathin insulating photoresist layer deposited on various types of conductive structures. A modified atomic force microscope (AFM) designed for local resistance measurements is used as a nanoindenter. The nanoindentation is performed while measuring continuously the resistance between the conductive tip of the AFM and the conductive layer, which is used as the trigger parameter to stop the indentation. This allows a very accurate control of the indentation process, The indented hole is subsequently filled by a metal to create a contact on the underlying layer. We show that nanocontacts; in the range of 1 to 10 nm(2) can be created with this technique.

We show that the electrodeposition of Ni80Fe20 on top of a thin aluminum oxide barrier leads to particle growth occurring on preferential nucleation centers. The particle sites are attributed to local defects in the aluminum oxide barrier. As a function of the thickness of the barrier, different growth modes can occur. For thinner barriers, new nucleation centers are created during electrodeposition. The resistance of the defects, characterized by conducting atomic force microscopy, ranges from less than 10(4) to greater than 10(12) Omega. Various I(V) characteristics were also obtained, depending on the resistance of the defect. These results suggest that this experimental technique could be a very interesting one with which to fabricate nanoconstrictions dedicated to ballistic magnetoresistance studies. (C) 2001 American Institute of Physics.