A luminescent molecular thermometer for long-term absolute temperature measurements at the nanoscale

El pdf del artículo es la versión post-print.A unique Eu3+/Tb3+ luminescent self-referencing nanothermometer allowing absolute measurements in the 10–350 K temperature range and sub-micrometer spatial resolution is reported (see Figure). It has up to 4.9%·K−1 temperature sensitivity and high photostability for long-term use. The combination of molecular thermometry, superparamagnetism and luminescence in a nanometric host matrix provides multifunctionality opening the way for new exciting applications.We acknowledge Fundação para a Ciência e a Tecnologia (FCT, Portugal), COMPETE and FEDER programs (PTDC/CTM/101324/2008) and Integrated Spanish-Portuguese Action PT2009–0131 for fi nancial support. The work in Zaragoza has been supported by the grants MAT2007–61621 and CONSOLIDER CSD2007–00010 from the Ministry of Education. CDSB (SFRH/BD/38472/2007) and PPL (SFRH/BPD/34365/2006) thank FCT for grants.Peer Reviewe

Influence of structural and magnetic properties in the heating performance of multicore bioferrofluids

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).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.R.B. would like to thank ICMA-CSIC for the JAE predoc grant. Financial support from Grant No. MAT2011-25991 is gratefully acknowledged. We acknowledge Fundaçâo para a Ciência e Tecnologia (FCT, Portugal), COMPETE, and FEDER programs (Pest-C/CTM/LA0011/2013). N.J.O.S. acknowledges FCT for the Ciência 2008 program.Peer Reviewe

Structural and magnetic studies in ferrihydrite nanoparticles formed within organic-inorganic hybrid matrices

6 pages, 6 figures, 1 table.We report detailed transmission electron microscopy, high resolution transmission electron microscopy (HRTEM), and scanning transmission electron microscopy/energy dispersive x-ray spectroscopy (STEM/EDS) studies on ferrihydrite nanoparticles in an organic-inorganic matrix. The Fourier transform of HRTEM images indicates the existence of six-line ferrihydrite. Combined STEM and EDS studies give further confirmation of the presence of iron in the observed particles and its absence in the matrix. The derived mean particle size and size distribution is 4.7±0.2 nm with a lognormal deviation of s=0.4±0.1. These values were used for analysis of magnetic measurements, yielding the determination of the anisotropy constant Keff=4×105 erg/cm3 and the power relation between the number of iron ions per particle and the number of uncompensated ones p≈1/3. This value indicates that the uncompensated spins are mainly randomly distributed at the surface. According to this model, a shell thickness of about one ferrihydrite unit cell is estimated.The financial support from FCT, POCTI/ CTM/46780/02, research grant MAT2004-03395-C02-01 from the Spanish CICYT, and Acción Integrada Luso- Española E-105/04 is gratefully recognized. One of the authors (N.J.O.S.) acknowledges a grant from FCT (Grant No. SFRH/BD/10383/2002). Another author (L.M.L.-M.) acknowledges support from Xunta de Galicia (Grant No. PGIDIT03TMT30101PR).Peer reviewe

Magnetic hyperthermia with ε-Fe2O3 nanoparticles

Biocompatibility restrictions have limited the use of magnetic nanoparticles for magnetic hyperthermia therapy to iron oxides, namely magnetite (Fe3O4) and maghemite (γ-Fe2O3). However, there is yet another magnetic iron oxide phase that has not been considered so far, in spite of its unique magnetic properties: ε-Fe2O3. Indeed, whereas Fe3O4 and γ-Fe2O3 have a relatively low magnetic coercivity, ε-Fe2O3 exhibits a giant coercivity. In this report, the heating power of ε-Fe2O3 nanoparticles in comparison with γ-Fe2O3 nanoparticles of similar size (∼20 nm) was measured in a wide range of field frequencies and amplitudes, in uncoated and polymer-coated samples. It was found that ε-Fe2O3 nanoparticles primarily heat in the low-frequency regime (20–100 kHz) in media whose viscosity is similar to that of cell cytoplasm. In contrast, γ-Fe2O3 nanoparticles heat more effectively in the high frequency range (400–900 kHz). Cell culture experiments exhibited no toxicity in a wide range of nanoparticle concentrations and a high internalization rate. In conclusion, the performance of ε-Fe2O3 nanoparticles is slightly inferior to that of γ-Fe2O3 nanoparticles in human magnetic hyperthermia applications. However, these ε-Fe2O3 nanoparticles open the way for switchable magnetic heating owing to their distinct response to frequency.This work was supported by European Union's Horizon 2020 FET Open program [Grants no: 801305 and 829162] Spanish Ministry of Science Innovation and Universities [Grant no: PGC2018_095795_B_I00] and Diputación General de Aragón [E11/17R]. Authors would like to acknowledge the use of Servicio General de Apoyo a la Investigación-SAI, Universidad de Zaragoza. This work was developed within the scope of the projects CoolPoint P2020-PTDC-CTMNAN-4511-2014 and CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the FCT/MEC and co-financed by FEDER under the PT2020 Partnership Agreement.We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).Peer reviewe

Co II/ZnII-(L-tyrosine) magnetic metal-organic frameworks

Three chiral coordination polymers assembled from L-tyrosine (L-tyr) and cobalt, cobalt/zinc and zinc salts, with a new three-dimensional (3D) structure and formulated as [M(L-tyr)] n (M = Co, Co/Zn, Zn) have been prepared by mild hydrothermal synthesis. These three compounds are isostructural, crystallize with monoclinic symmetry in the C2 space group and possess four crystallographically unique metal sites in tetrahedral (two) and octahedral (two) coordination environments resulting in two slightly distinct edge-sharing metal dimers with L-tyr linking the metal atoms in pillars. These features result in a dense framework. The study of the magnetic properties of the cobalt-bearing solid reveals a ferromagnetic exchange interaction within the Co 2+ dimers. The racemic compound of dl-tyrosine and cobalt was also synthesized and its structure characterized. The crystal structure of chiral isomorphous metal-organic frameworks, [M(L-tyrosine)]n, (M = Co, Zn, Co/Zn) features tetrahedral and octahedral metal sites, resulting in two slightly different edge-sharing metal dimers, with L-tyrosine linking the metal atoms in pillars and forming a dense framework. In the dimers, a ferromagnetic exchange interaction couples the Co 2+ ions. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.We acknowledge Fundação para a Ciência e a Tecnologia, Fundo Social Europeu, Ciencia 2007, Fundo Europeu de Desenvolvimento Regional (FEDER), Quadro de Referência Estratégico Nacional (QREN), COMPETE (grants PEst-C/CTM/LA0011/2011, PTDC/QUI/ 65805/2006, FCOMP-01-0124-FEDER-007424 and SFRH/BPD/43789/2008). The Aveiro-Zaragoza collaboration was supported by the Integrated Spanish-Portuguese Action (grant PT2009-0131). The work in Zaragoza was supported by the Ministry of Economy and Competitivity through grants MAT2007-61621, MAT2011-27233-C02-02 and CONSOLIDER CSD2007-00010.Peer Reviewe

Estimating spontaneous magnetization from a mean field analysis of the magnetic entropy change

The magnetocaloric effect is a common property of all magnetic systems, corresponding to a temperature change under adiabatic conditions (ΔTad) or achange in magneticentropy in isothermal conditions (ΔSM), for a given applied magneticfieldchange. ΔTad can be directly measured under adiabatic conditions and indirectly estimated from specific heat measurements. ΔSM can be indirectly estimated from specific heat measurements or magnetization measurements (the usual approach). Early work on the study of ferromagnets used direct measurements of ΔTad to determine the spontaneousmagnetization for a given temperature value. In this work, we use ΔSM obtained from isothermal magnetization measurements to estimate the spontaneousmagnetization, comparing this result to mean-field fittings from a novel scaling method, discussing the validity and usefulness of this approach from considerations from the Landau theory of phase transitions.The authors would liketo acknowledge the financial support from FCT, (CERN/FP/83643/2008 and POCI/CTM/61284/2004) and Ph.D. Grant SFRH/BD/17961/2004, and from CICYT(grant MAT2007-61621).Peer Reviewe

Neutron diffraction and magnetism of CoO antiferromagnetic nanoparticles

We report a study on neutron diffraction and magnetic properties ol cobalt oxide CoO antiferromagnetic nanoparticles with different sizes. The nanoparticles are composed by a structurally and magnetically ordered core and a structurally ordered and magnetically disordered shell with a thickness of about 2 nm. The ordered core has cell parameters, moments direction and modulus similar to those of bulk CoO. Small differences found are attributed to an increase of the oxidation of the nanoparticles with the decrease of size. A remanent moment Mr can be induced in CoO nanoparticles by crossing the transition temperature in the presence of a magnetic field, while the magnetic structure of the antiferromagnetically ordered moments of the nanoparticles core remains unchanged after field cooling within the experimental precision, suggesting that Mr arises in the magnetically disordered shell.The iberian collaboration is supported by the Integrated Spanish- Portuguese Action PT2009-0131. The work in Zaragoza has been supported by the research grants MAT2007-61621, MAT2009-13977-C03-01 and CONSOLIDER CSD2007-00010 from the Ministry of Education. N J O S acknowledges FCT for Ciencia 2008 program.Peer Reviewe

Texture-induced magnetic interactions in ferrofluids

We report a method for reversibly controlling the strength of dipole-dipole interactions in maghemite ferrofluids. In order to induce some magnetic texture, the ferrofluid is exposed to a strong magnetic field while it is cooled from room temperature to below its freezing temperature. The experimental data show that the average strength of dipolar interactions increases with increasing texture and that the magnetic relaxation becomes slower. © 2012 American Institute of Physics.This work has been funded by the Spanish MICINN and FEDER, Projects Nos. MAT2007-61621, MAT2009-13977-C03 (MOLCHIP), and CONSOLIDER-INGENIO CSD 2007-00010. A.U. and A.A. thank the European Network MAGMANet and the Spanish MICINN (FPI program), respectively, for their scholarships.Peer Reviewe

Pressure effects in hollow and solid iron oxide nanoparticles

arXiv:1301.5708v1We report a study on the pressure response of the anisotropy energy of hollow and solid maghemite nanoparticles. The differences between the maghemite samples are understood in terms of size, magnetic anisotropy and shape of the particles. In particular, the differences between hollow and solid samples are due to the different shape of the nanoparticles and by comparing both pressure responses it is possible to conclude that the shell has a larger pressure response when compared to the core. © 2013 Elsevier B.V.The Aveiro–Barcelona collaboration has been supported by the Integrated Spanish–Portuguese Action under the Grant no. AIB2010PT-00099. The Aveiro–Zaragoza collaboration has been supported by the Integrated Spanish–Portuguese ActionPT2009-0131. The work in Zaragoza has been supported by the research Grants MAT2011-27233-C02-02, MAT2011-25991 and CONSOLIDER CSD2007-00010 from the Ministry of Education. The financial support of the CSIC and Spanish Ministerio de Ciencia e Innovación (PI201060E013) is also acknowledged. The work in Japan was supported by a Grant-in-Aid for Scientific Research (C) (No. 23550158) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. Ò.I. and A.L. acknowledge funding of the Spanish MICINN through Grant nos. MAT2009-08667 and CSD2006-00012, and Catalan DIUE through Project no. 2009SGR856. N.J.O.S. acknowledges FCT for Ciencia 2008 program.Peer Reviewe

Heat transfer studies using Ln3+ based nanothermometers

Trabajo presentado al: "Eurotherm 103: Nanoscale and Microscale Heat Transfer IV" celebrado en Lyon (Francia) del 15 al 17 de octubre de 2014.There is an increasing demand for accurate, non-invasive and self-reference temperature measurements as technology progresses into the nanoscale. This is particularly so in micro and nanofluidics where the comprehension of heat transfer and thermal conductivity mechanisms can play a crucial role in areas as diverse as energy transfer and cell physiology. In fact, the integration of optics and micro/nanofluidic devices to provide novel functionalities in nanosystems is stimulating a promising new area of optofuidics, for nanomedicine and energy. Despite promising progress precision control of fluid temperature by accounting for local temperature gradients, heat propagation and accurate temperature distributions have not yet been satisfactorily addressed, e.g., investigating heat transfer mechanisms in nanofluids or mapping temperature distributions within living cells. With the objective of investigate the heat transfer mechanisms in nanofluids and mapping temperature distributions we have focused in the development and characterization of nanothermometers that can be dispersed in different base fluids or incorporate organicinorganic hybrid films. The thermometers performance can be compared using the relative sensitivity, defined as the relative change on the thermometric parameter, the spatial resolution (δx) and the temporal resolution (δt) the largest temporal and spatial temperature change measured. In 2013 we reported the development of two luminescent ratiometric nanothermometers based on a γ-Fe2O3 maghemite core coated with an organosilica shell co-doped with Eu3+ and Tb3+ β-diketonate chelates. The design of either the siloxane-based hybrid host or the chelate ligands permits the nanothermometers to be used in nanofluids (i.e. water suspensions of the nanothermometers) at 293–320 K with an emission quantum yield between 0.24 ± 0.02 and 0.38 ± 0.04, a relative sensitivity of up to 1.5% K-1 (at 293 K), a spatiotemporal resolution (constrained by the experimental setup) of (64–65) µm/150 ms (to move out of the temperature uncertainty, δT, stated as 0.4 K). When illuminated with UV light, the thermometric nanofluids are able to map the temperature.None of luminescent devices proposed so far can map the temperature in a micro/nanofluid in the 293–320 K range with such high emission quantum yields, relative sensitivity, temperature uncertainty, and spatio-temporal resolution values. Furthermore, a velocity in of heat traveling within the nanofluid, (2.2 ± 0.1) mm s-1, was determined at 294 K simply using the Eu3+/Tb3+ steady-state spectra of the nanothermometers.The work is partially supported by FCT Project RECI/CTM-CER/0336/2012 and FEDER, ref COMPETE: FCOMP-01-0124-FEDER-027465. CDSB tanks FCT (SFRH/BPD/ 89003/ 2012) for a grant.Peer Reviewe