The effect of the magnetically dead layer on the magnetization and the magnetic anisotropy of the dextran-coated magnetite nanoparticles

We present a study on the magnetic behavior of dextran-coated magnetite nanoparticles (DM NPs) with sizes between 3 and 19 nm, synthesized by hydrothermal-assisted co-precipitation method. The decrease of saturation magnetization (M-s) with decreasing particle size has been modeled by assuming the existence of a spin-disordered layer at the particle surface, which is magnetically dead. Based on this core-shell model and taking into account the weight contribution of non-magnetic coating layer (dextran) to the whole magnetization, the dead layer thickness (t) and saturation magnetization M-s of the magnetic cores in our samples were estimated to be t = 6.8 angstrom and M-s = 98.8 emu/g, respectively. The data of M-s were analyzed using a law of approach to saturation, indicating an increase in effective magnetic anisotropy (K-eff) with decreasing the particle size as expected from the increased surface/volume ratio in small MNPs. The obtained K-eff values were successfully modeled by including an extra contribution of dipolar interactions due to the formation of chain-like clusters of MNPs. The surface magnetic anisotropy (K-s) was estimated to be about K-s = 1.04x10(5) J/m(3). Our method provides a simple and accurate way to obtain the M-s core values in surface-disordered MNPs, a relevant parameter required for magnetic modeling in many applications. GRAPHICS]

Mapping local patterns of childhood overweight and wasting in low- and middle-income countries between 2000 and 2017

A double burden of malnutrition occurs when individuals, household members or communities experience both undernutrition and overweight. Here, we show geospatial estimates of overweight and wasting prevalence among children under 5 years of age in 105 low- and middle-income countries (LMICs) from 2000 to 2017 and aggregate these to policy-relevant administrative units. Wasting decreased overall across LMICs between 2000 and 2017, from 8.4% (62.3 (55.1–70.8) million) to 6.4% (58.3 (47.6–70.7) million), but is predicted to remain above the World Health Organization’s Global Nutrition Target of <5% in over half of LMICs by 2025. Prevalence of overweight increased from 5.2% (30 (22.8–38.5) million) in 2000 to 6.0% (55.5 (44.8–67.9) million) children aged under 5 years in 2017. Areas most affected by double burden of malnutrition were located in Indonesia, Thailand, southeastern China, Botswana, Cameroon and central Nigeria. Our estimates provide a new perspective to researchers, policy makers and public health agencies in their efforts to address this global childhood syndemic

A novel method for <i>in situ</i> encapsulation of curcumin in magnetite-silica core-shell nanocomposites:A multifunctional platform for controlled drug delivery and magnetic hyperthermia therapy

In this study, we developed a novel strategy for in situ encapsulation of hydrophobic drugs such as curcumin into the magnetite-mesoporous silica nanocomposites with a core-shell structure. In the proposed method, a modified reverse microemulsion system was used for silica formation on the surface of curcumin-loaded Fe3O4 nanoparticles (Cur@Fe3O4 NPs) to render mesoporous silica-coated Cur@Fe3O4 NPs (SiO2/Cur@Fe3O4 NPs). The prepared SiO2/Cur@Fe3O4 NPs with a core-shell structure had a spherical shape with a mean particle size less than 100 nm. The heating efficacy of the prepared nanocomposites was examined for application in magnetic hyperthermia therapy by exposing them to different biological safe alternating magnetic fields. The maximum specific absorption rate (SAR) obtained by the prepared sample, was found to be 22.11 WgFe3O4−1at the magnetic field intensity of 28 kA m−1 and frequency of 120 kHz.. Also, the prepared nanocomposites exhibited a pH-responsive drug release behavior. The in vitro drug release studies showed that, only 8.9% of curcumin was releasedwas from SiO2/Cur@Fe3O4 NPs at pH 7.4, while about 40% of drug was released at pH 5.0, after 5 days. Moreover, the in vitro cytotoxicity analysis showed that, by encapsulation of curcumin in the prepared nanocomposites, the cytotoxicity of the drug was significantly increased against breast cancer MCF-7 cells, compared to the free drug, so that, at curcumin concentration of 40 μg mL−1, the viability of MCF-7 cells incubated with free curcumin was 62.0%, whereas by encapsulation of curcumin in SiO2/Cur@Fe3O4 NPs the viability was decreased to 26.7% (Pvalue ≤ 0.005)

Optical fiber sensor based on magneto-plasmonic features of Ag-Co nanostructure for ppm ammonium detection in aqueous solutions

This is an accepted manuscript of an article published by Elsevier in Optical Fiber Technology on 03/11/2021, available online: https://doi.org/10.1016/j.yofte.2021.102730 The accepted version of the publication may differ from the final published version.Magneto-plasmonic nanocomposite deposition enables fiber optic sensors to detect water pollution caused by chemical contaminants of ammonium that is harmful to human and aquatic organisms as well. In this study, Ag-Co nanocomposite was deposited on unclad multimode glass fiber to distinguish the ammonium concentration in the aqueous medium. Prior to the fabrication of the fiber probe, for finding the stronger surface plasmon resonance (SPR) effect, Ag-Co nanocomposite (which had different structures) was deposited on the glass prism. The maximum SPR shift of 7.16° was observed by varying the ammonium concentration from 0 to 80 ppm, when Ag was deposited as the outer layer and Co acted as the inner layer. The working principle of the sensor was based on manipulating the analyte viscosity with the magnetization of Co nanolayer exposed to the external magnetic field and adjusting the SPR conditions via the interaction of different ammonium concentrations with the Ag layer. Spectral wavelength and the intensity interrogation technique in the visible region confirmed the detection of ammonium in the solution with sensitivity, response time, limit of detection (LOD), and recovery time of 0.131 nm/ppm, 17 s, 2.9 ppm, and 12 s, respectively. These features together with a high selectivity make the proposed sensor a potential candidate for determining the environmental pollution, controlling the industrial safety requirements, and accurately measuring the water quality in daily life.Published versio

Folic acid-conjugated dextran-coated Zn0.6Mn0.4Fe2O4 nanoparticles as systemically delivered nano heaters with self-regulating temperature for magnetic hyperthermia therapy of liver tumors

Abstract Successful cancer treatment using magnetic hyperthermia therapy (MHT) strongly depends on biocompatible magnetic nanoparticles (NPs). They can effectively accumulate in tumor tissues after systemic injection and generate heat in the therapeutic temperature range (42–48 °C) by exposure to an AC magnetic field (AMF). For this purpose, folic acid-conjugated dextran-coated Zn0.6Mn0.4Fe2O4 (FA-Dex-ZMF) NPs were synthesized as smart nano heaters with self-regulating temperatures for MHT of liver tumors. Animal studies on BALB/c mice showed that the prepared NPs did not cause acute toxicity upon administration up to 100 mg kg−1. Likewise, no significant changes in hematological and biochemical factors were observed. FA-Dex-ZMF NPs were studied by exposing them to different safe AC magnetic fields (f = 150 kHz, H = 6, 8, and 10 kA m−1). Calorimetric experiments revealed that the NPs reached the desired temperature range (42–48 °C), which was suitable for MHT. Moreover, the efficacy of FA-Dex-ZMF NPs in MHT of liver tumors was investigated in vivo in liver-tumor-bearing mice. The obtained results revealed that the average volume of tumors in the control group increased 2.2 times during the study period. In contrast, the tumor volume remained almost constant during treatment in the MHT group. The results indicated that folic acid-conjugated dextran-coated Zn0.6Mn0.4Fe2O4 NPs with self-regulating temperature could be a promising tool for systemically delivered MHT