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The formation mechanism of α″-Fe16N2 phase was investigated in the form of nanoparticles. Both α-Fe and γ-Fe2O3 nanoparticles were used to prepare α″-Fe16N2 by using a low-temperature nitriding process (≤180 °C). The synthesized α″-Fe16N2 nanoparticles have a high α″-Fe16N2 volume ratio up to 93%, with a specific saturation magnetization of 178 emu/g (room temperature) and coercivity of 2.0 kOe. The formation of α″-Fe16N2 phase includes three stages: (1) the heterogenous nucleation of α″-Fe16N2 with simultaneous chemical reaction, (2) the growth of α″-Fe16N2 with a local electric field in the Fe16N2 layer, and (3) the termination of Fe16N2 growth due to the nucleation of other Fe–N phases (ε-Fe3N or γ′-Fe4N). In low-temperature nitriding, NH3 was used as the nitrogen source. The adsorbed NH3 molecules on the Fe surface decompose into N and H atoms, and then N atoms react with Fe and nucleation of α″-Fe16N2 simultaneously occurs at the high-energy surface sites of reduced Fe nanoparticles. The growth of α″-Fe16N2 phase can be explained by the electric field modified diffusion theory, where the electric field is established by the migration of Fe and N ions and electrons. Finally, the nucleation of Fe–N stable phases (ε-Fe3N or γ′-Fe4N) ceases the further growth of α′′-Fe16N2 layer. Then, there is critical thickness for the α″-Fe16N2 layer, which is estimated to be 10–15 nm from the surface. Therefore, single-phase α″-Fe16N2 nanoparticles are expected in fine particles with less than 30 nm in diameter. [ABSTRACT FROM AUTHOR]

Well‐defined nanostructures are crucial for precisely understanding nano‐bio interactions. However, nanoparticles (NPs) fabricated through conventional synthesis approaches often lack poor controllability and reproducibility. Herein, a synthetic biology‐based strategy is introduced to fabricate uniformly reproducible protein‐based NPs, achieving precise control over heterogeneous components of the NPs. Specifically, a ferritin assembly toolbox system is developed that enables intracellular assembly of ferritin subunits/variants in Escherichia coli. Using this strategy, a proof‐of‐concept study is provided to explore the interplay between ligand density of NPs and their tumor targets/penetration. Various ferritin hybrid nanocages (FHn) containing human ferritin heavy chains (FH) and light chains are accurately assembled, leveraging their intrinsic binding with tumor cells and prolonged circulation time in blood, respectively. Further studies reveal that tumor cell uptake is FH density‐dependent through active binding with transferrin receptor 1, whereas in vivo tumor accumulation and tissue penetration are found to be correlated to heterogeneous assembly of FHn and vascular permeability of tumors. Densities of 3.7 FH/100 nm2 on the nanoparticle surface exhibit the highest degree of tumor accumulation and penetration, particularly in tumors with high permeability compared to those with low permeability. This study underscores the significance of nanoparticle heterogeneity in determining particle fate in biological systems. [ABSTRACT FROM AUTHOR]

Highlights • Directly characterize the M s and D of SPMNPs in liquid phase. • R is proportional to T and negatively correlated with A L , M s , and D. • R is independent of SPMNP ferrofluid concentration and volume. • A method to characterize the physical and magnetic properties of SPMNPs. • Can be applied as building blocks in nanoparticle characterization devices. Abstract Superparamagnetic nanoparticles (SPMNPs), with unique physical and magnetic properties that differentiate them from their bulk magnetic materials, have been widely studied for potential applications in biomedical areas. With proper surface chemical functionalization, SPMNPs have found their applications in magnetic hyperthermia therapy, magnetic bioassays, drug delivery, magnetic manipulation, etc. These applications require elaborate tuning of the physical and magnetic properties of the SPMNPs such as saturation magnetization M s and magnetic core size D. In this work, we present a search coil-based method to directly characterize the M s of SPMNPs in the liquid phase. The nonlinear magnetic responses of SPMNPs under oscillating magnetic fields are exploited and the induced harmonic signals are used to analyze their M s and D. Different combinations of M s and D are assumed and their harmonic ratios R are summarized. Curve fitting shows that the harmonic ratio R = 0.74 + 2.85 × 10 9 ∙ D - 4.41 ∙ M s - 1.44 , with the coefficient of determination R-square = 0.98. [ABSTRACT FROM AUTHOR]

In this paper, we propose and demonstrate a Brownian relaxation-based mixing-frequency method to test sample viscosities. This method uses excitatory and detection coils and Brownian relaxation-dominated superparamagnetic nanoparticles, which are sensitive to the characteristics of the liquid environment such as viscosity. Oscillating magnetic fields can induce harmonics through the nonlinear magnetization curve of superparamagnetic nanoparticles. Phase lag of the third-harmonic signal and the induced voltage ratio of the fifth over the third harmonic signals are collected. We build up standard graphs by plotting collected data from eight magnetic nanoparticle (MNP) mixtures with different viscosities. For any unknown liquids mixed with MNPs, we can collect phase lag and voltage ratio information and insert these data into the aforementioned standard graphs. This in vitro viscosity test can be done in 1 min. Our experimental result showed a 0.3% error rate for the liquid viscosity test. [ABSTRACT FROM PUBLISHER]

Abstract: We present a systemic study on the structural, thermal and magnetic properties of Zn1−x Mn x O nanoparticles synthesized by a combustion method with heavily Mn doping concentrations x=0.05, 0.15 and 0.25. The structural evolutions in relation to the possible variation of the Mn oxidation state and dopant induced tiny Zn2MnO4/Mn2O3 and ZnMnO3/MnO2 impurities, which have not been detected by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM), were investigated by means of X-ray photoelectron spectroscopy (XPS), Raman scattering spectra, thermo-gravimetric analysis (TGA) and magnetic measurements. It is evidenced that the optimal Mn concentration x in ZnO to grow single phase Zn1−x Mn x O should be below the cation percolation threshold x p (about 0.125), which is the basis to form real diluted magnetic semiconductors (DMSs). [Copyright &y& Elsevier]

Superparamagnetic nanoparticles (MNPs) have been utilized in biomedical sensing, detection, therapeutics, and diagnostics due to their unique magnetic response under different driving fields. In this letter, we report a multi-tracer tracking method that uses different kinds of MNPs as magnetic tracers along with two alternating magnetic fields that can be potentially used to build magnetic-based flow cytometry. By applying two driving fields at frequency fH and fL to MNPs, the response signal is measured at the combinatorial frequencies such as fH±2fL (3rd harmonics), fH±4fL (5th harmonics), fH±6fL (7th harmonics), and so on. Each MNP has its own signature of phase and amplitude, and it is possible to differentiate individual MNPs in a mixture. We theoretically demonstrated colorizing up to 4-MNP tracers in one mixture with an error rate lower than 10%. The performance of multi-tracer imaging can be optimized by increasing the driving field frequency, choosing MNPs with higher saturation magnetization, and using MNP tracers with more centralized size distribution. [ABSTRACT FROM AUTHOR]