AuFe Alloys Research Articles

FeAu Bimetallic Nanoparticle as Fe(0) Reservoir for Near Infrared Laser Enhanced Ferroptosis/Pyroptosis‐Based Tumor Immunotherapy

AbstractIron (Fe)‐based nanoparticles (NPs) have attracted considerable attention in nanomedicine research due to their enhancement effects in magnetic resonance imaging (MRI) and cancer therapy. Although zero‐valent Fe (Fe(0)) can serve as an active catalyst to decompose H2O2 into reactive oxygen species (ROS), its activity is compromised in physiological conditions due to its susceptibility to oxidation. Here it is reported that a 9 nm FeAu alloy NP system can efficiently stabilize Fe(0) in neutral pH solution, but release Fe(0) in tumor‐bearing environment, catalyzing H2O2 decomposition to ROS. Although Fe3O4 NPs and Au NPs are well‐known for their biocompatible, FeAu NPs effectively eliminate cancer cells at an IC50 as low as 15 µg mL−1 Fe. Further proteomics analysis reveals that FeAu NPs can concomitantly induce both ferroptosis and pyroptosis. Additional near‐infrared (NIR) irradiation further increases cell death and promotes maturation of dendritic cells within tumor‐draining lymph nodes and infiltration of helper T cells and cytotoxic T lymphocytes within tumor sites, resulting in significant reduction in tumor growth and metastasis. The studies demonstrate a great potential of FeAu NPs as a stable Fe(0) reservoir for pH/NIR controlled Fe(0) release and further for ferroptosis and pyroptosis co‐mediated tumor immunotherapy.

Formation of metastable phases during spark plasma sintering of Fe@Au core–shell particles

ABSTRACT The present work reports the formation of Fe-Au metastable alloys by galvanic replacement, pressureless spark plasma sintering (SPS) and acid treatment. The reaction of partial galvanic replacement between micrometer-sized iron particles and HAuCl4 solution allowed synthesising core–shell Fe@Au particles. When the Fe@Au particles were treated in HCl solution, iron was selectively dissolved and hollow Au particles were formed. Pressureless SPS of the Fe@Au core–shell particles led to the formation of a metastable intermetallic phase, FeAu3, and a supersaturated solid solution, Au(Fe). The latter was resistant to HCl solution; at the same time, the FeAu3 phase decomposed during HCl treatment to form a porous gold structure. This work shows that a combination of galvanic replacement, SPS and acid treatment can be used for the preparation of metastable Fe-Au alloys with different phase compositions and particle morphologies.

The effect of micromechanical stresses on vacancy formation and stress-driven mass-transport in polycrystalline Fe–Au alloy

In recent years, a new class of super saturated binary and ternary alloys have demonstrated the ability for the self-healing of creep-induced voids formed at the grain boundaries. However, a clear understanding of the parameters affecting the self-healing mechanism is still not yet complete. One of the main challenges is understanding the effect of microstructure and micromechanical stresses on the redistribution of the healing-solute and vacancies. To this end, we address this issue using a CALPHAD-informed diffusion model coupled with crystal plasticity. In principle, the approach is general and can be used for any binary Fe–X alloy, but in this work Fe–Au binary system is used since it experimentally showed the best healing efficiency. First, we present a multicomponent diffusion model considering cross and stress-driven diffusion. The effect of stress was also considered on the equilibrium vacancy concentration. To investigate the effect of the micromechanical stresses, a representative volume element (RVE) was obtained using the phase-field method. The results showed that the maximum vacancy concentration is at the grain boundaries (GBs) with the highest hydrostatic tensile stresses. These were also the regions of the highest Au enrichment. A crucial factor to achieve this is the high diffusivity of Au compared to the Fe matrix. Increasing the stresses, lead to an increase both in vacancy and Au concentration. The accompanying increased stress triaxiality is suggested to be the reason for the reduced self-healing efficiency observed in previous experimental studies.

Cytotoxicity of PEG-Coated Gold and Gold–Iron Alloy Nanoparticles: ROS or Ferroptosis?

Nanomedicine relies on the exploitation of nanoscale constructs for therapeutic and diagnostic functions. Gold and gold–iron alloy nanoparticles (NPs) are two examples of nanomaterials with favorable features for use in nanomedicine. While gold NPs have been studied extensively in the last decades, they are not biodegradable. Nonetheless, biodegradation was recently observed in gold alloys with iron obtained using laser ablation in liquid (LAL). Hence, there is a significant interest in the study of the biological effects of gold and gold–iron alloy nanoparticles, starting from their tolerability and cytotoxicity. In this study, these two classes of NPs, obtained via LAL and coated with biocompatible polymers such as polyethylene glycol, were investigated in terms of their cytotoxicity in fibroblasts, prostate cancer cells (PC3) and embryonic kidney cells (HEK). We also explored the effects of different synthetic procedures, stabilizing additives, and the possible mechanisms behind cell mortality such as the formation of reactive oxygen species (ROS) or ferroptosis. NPs larger than 200 nm were associated with lower cell tolerability. The most tolerable formulations were pure PEG-Au NPs, followed by PEG-Au–Fe NPs with a hydrodynamic size < 50 nm, which displayed a toxicity of only 20% in fibroblasts after 72 h of incubation. In addition, tumor cells and highly proliferating HEK cells are more sensitive to the NPs than fibroblasts. However, a protective effect of catalase was found for cells incubated with PEG-Au–Fe NPs, indicating an important role of hydrogen peroxide in alloy NP interactions with cells. These results are crucial for directing future synthetic efforts for the realization of biocompatible Au NPs and biodegradable and cytocompatible Au–Fe alloy NPs. Moreover, the correlation of the cytocompatibility of NPs with ROS and ferroptosis in cells is of general interest and applicability to other types of nanomaterials.

The exceptional performance of the plasmonic Au-Fe/TiO2 nanocatalysts achieved by O2 plasma activation

The plasmonic Au-based bimetallic nanocatalysts have the potential to exhibit superior visible-light (VL) photocatalytic activity, and their performance in reaction is greatly dependent on the method of activation. Herein, Au-Fe/TiO2 nanocatalysts are prepared by a modified incipient wetness impregnation method with the precursors of HAuCl4 and FeCl3. The visible-light activities of the samples activated by calcination at 300 °C, 50%H2/Ar plasma and O2 plasma are compared using CO oxidation. Au-Fe/TiO2 activated by O2 plasma has the most exceptional performance with a CO conversion of 90%. The samples are characterized by transmission electron microscopy, UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectra, and CO chemisorption. It is found that O2 plasma restructures nano Au and Fe on the TiO2 support into Au-Fe alloy, preventing nano Au particle size increase. The Au-Fe alloy nanoparticles on TiO2 has a narrow size distribution and are approximately 4 nm in size. Many surface oxygen species on Au-Fe alloy are observed, as well as a unique board peak assigned to CO adsorption, and they can improve the activity and stability of Au-Fe alloy in CO oxidation. Finally, a reaction mechanism of Au-Fe/TiO2 activated by O2 plasma for CO oxidation is developed. This research demonstrates that the treatment of O2 plasma is an available approach to producing efficient Au-Fe plasmonic nanocatalysts.

Theranostic doxorubicin encapsulated FeAu alloy@metal-organic framework nanostructures enable magnetic hyperthermia and medical imaging in oral carcinoma

Metal-organic frameworks (MOFs) have emerged as attractive candidates in cancer theranostics due to their ability to envelop magnetic nanoparticles, resulting in reduced cytotoxicity and high porosity, enabling chemodrug encapsulation. Here, FeAu alloy nanoparticles (FeAu NPs) are synthesized and coated with MIL-100(Fe) MOFs to fabricate FeAu@MOF nanostructures. We encapsulated Doxorubicin within the nanostructures and evaluated the suitability of this platform for medical imaging and cancer theranostics. FeAu@MOF nanostructures (FeAu@MIL-100(Fe)) exhibited superparamagnetism, magnetic hyperthermia behavior and displayed DOX encapsulation and release efficiency of 69.95 % and 97.19 %, respectively, when stimulated with alternating magnetic field (AMF). In-vitro experiments showed that AMF-induced hyperthermia resulted in 90 % HSC-3 oral squamous carcinoma cell death, indicating application in cancer theranostics. Finally, in an in-vivo mouse model, FeAu@MOF nanostructures improved image contrast, reduced tumor volume by 30-fold and tumor weight by 10-fold, which translated to enhancement in cumulative survival, highlighting the prospect of this platform for oral cancer treatment.

Structural evolution under physical and chemical stimuli of metastable Au-Fe nanoalloys obtained by laser ablation in liquid.

Metastable alloy nanoparticles are investigated for their variety of appealing properties exploitable for photonics, magnetism, catalysis and nanobiotechnology. Notably, nanophases out of thermodynamic equilibrium feature a complex "ultrastructure" leading to a dynamic evolution of composition and atomic arrangement in response to physical-chemical stimuli. In this manuscript, metastable Au-Fe alloy nanoparticles were produced by laser ablation in liquid, an emerging versatile synthetic approach for freezing multielement nanosystems in non-equilibrium conditions. The Au-Fe nanoalloys were characterized through electron microscopy, elemental analysis, X-ray diffraction and Mössbauer spectroscopy. The dynamics of the structure of the Au-Fe system was tracked at high temperature under vacuum and atmospheric conditions, evidencing the intrinsic transformative nature of the metastable nanoalloy produced by laser ablation in liquid. This dynamic structure is relevant to possible application in several fields, from photocatalysis to nanomedicine, as demonstrated through an experiment of magnetic resonance imaging in biological fluids.

Boosted photothermal hydrogenation of acetylene on an efficient Au–Fe alloy catalyst

A chloroform-assisted method has been developed to prepare Au–Fe alloy catalysts under mild conditions, and they exhibit an excellent activity in the photothermal hydrogenation of acetylene.

The Magnetic Susceptibility of Alloys Below the Percolation Threshold

Within the theory of random interaction fields, the possibility of determining the Curie point and the paramagnetic Curie point corresponding to the appearance of short-range order is shown. In ferromag-netic alloys, there is a concentration range in which the long-range order is destroyed, but the short-range order persists. This leads to the appearance of a cluster glass phase, which is characterized by a time depen-dence of the magnetic susceptibility and the appearance of viscous magnetization. For an AuFe alloy as an example, the behavior of the initial magnetic susceptibility as a function of temperature and concentration is studied and compared with experimental data.

Interwire and Intrawire Magnetostatic Interactions in Fe-Au Barcode Nanowires with Alternating Ferromagnetically Strong and Weak Segments.

Metallic barcode nanowires (BNWs) composed of repeating heterogeneous segments fabricated by template-assisted electrodeposition can offer extended functionality in magnetic, electrical, mechanical, and biomedical applications. The authors consider such nanostructures as a 3D system of magnetically interacting elements with magnetic behavior strongly affected by complex magnetostatic interactions. This study discusses the influence of geometrical parameters of segments on the character of their interactions and the overall magnetic behavior of the array of BNWs having alternating magnetization, because the Fe and Au segments are made of Fe-Au alloys with high and low magnetizations. By controlling the applied current densities and the elapsed time in the electrodeposition, the dimension of the Fe-Au BNWs can be regulated. This study reveals that the influence of the length of magnetically weak Au segments on the interaction field between nanowires is different for samples with magnetically strong 100 and 200 nm long Fe segments using the first-order reversal curve (FORC) diagram method. With the help of micromagnetic simulations, three types of magnetostatic interactions in the BNW arrays are discovered and analy. This study demonstrates that the dominating type of interaction depends on the geometric parameters of the Fe and Au segments and the interwire and intrawire distances.

Single-Step Fabrication of Au-Fe-BaTiO3 Nanocomposite Thin Films Embedded with Non-Equilibrium Au-Fe Alloyed Nanostructures.

Nanocomposite thin film materials present great opportunities in coupling materials and functionalities in unique nanostructures including nanoparticles-in-matrix, vertically aligned nanocomposites (VANs), and nanolayers. Interestingly the nanocomposites processed through a non-equilibrium processing method, e.g., pulsed laser deposition (PLD), often possess unique metastable phases and microstructures that could not achieve using equilibrium techniques, and thus lead to novel physical properties. In this work, a unique three-phase system composed of BaTiO3 (BTO), with two immiscible metals, Au and Fe, is demonstrated. By adjusting the deposition laser frequency from 2 Hz to 10 Hz, the phase and morphology of Au and Fe nanoparticles in BTO matrix vary from separated Au and Fe nanoparticles to well-mixed Au-Fe alloy pillars. This is attributed to the non-equilibrium process of PLD and the limited diffusion under high laser frequency (e.g., 10 Hz). The magnetic and optical properties are effectively tuned based on the morphology variation. This work demonstrates the stabilization of non-equilibrium alloy structures in the VAN form and allows for the exploration of new non-equilibrium materials systems and their properties that could not be easily achieved through traditional equilibrium methods.

Circular dichroism of one-dimensional chain of Au-Fe alloy nanoparticles for refractive index sensing applications

Circular dichroism of one-dimensional chain of Au-Fe alloy nanoparticles for refractive index sensing applications

Study of the FCC-BCC phase transition in an Au-Fe alloy

The properties of the disordered Au-Fe substitution alloy are studied based on the analytical method, which uses the paired interatomic potential of Mie--Lennard-Jones. The parameters of the interatomic potential for the FCC and BCC structures of Au and Fe are determined. Based on these parameters, the concentration dependences of the properties of the FCC and BCC structures of the Au-Fe alloy are calculated. Under normal conditions (i.e., pressure P=0 and temperature T=300 K), changes in the properties of the Au-Fe alloy at the structural phase transition of FCC-BCC are calculated. Using the RP-model of the nanocrystal, the displacement of the Cf concentration, at which the FCC-BCC phase transition occurs, due to a decrease in the size of the nanoparticle was calculated. It is shown that at an isochoric-isothermal decrease in the number of atoms (N) in an Au-Fe nanoparticle, the Cf value displace towards higher Fe concentrations. For a nanoparticle with a fixed number of atoms and a constant surface shape, the Cf value increases at an isochoric increase in temperature, and the Cf value decreases at an isothermal decrease in density. Calculations have shown that at N<59900 for the Au1-CFeC alloy at P=0, T≤300 K and at any iron concentration, the FCC structure is more stable than the BCC structure. Keywords: gold, iron, substitution alloy, phase transition, state equation, elastic modulus, thermal expansion, nanoparticle, surface energy.

The chiral anomalous Hall effect at high magnetic fields in Au-Fe alloys

ABSTRACT The Hall effect of the disordered and frustrated magnetic alloys Au-Fe 8 at% and Au-Fe 18 at% was studied in applied magnetic fields up to 14 T. The measurements were carried out in fixed temperatures spanning the spin glass and paramagnetic phases of Au-Fe 8 at% and in the reentrant, ferromagnetic and paramagnetic states in Au-Fe 18 at%. The experiments confirm the occurrence of a large contribution from spin chiralities to the anomalous Hall effect (AHE) in both systems, either in the spin glass and the canted ferromagnetic phases. The amplitude of the chirality-driven term is progressively attenuated as the field intensity is increased. This effect is consistent with the expected field-induced closing of the solid angle defining scalar spin chirality. Evidence for the occurrence of a chiral contribution to AHE was also detected in the paramagnetic phases of the two studied systems, showing that this term persists as long as the typical time scale for the spin dynamics is significantly larger than the transport relaxation time.

Changes in the structure of the Au–Fe alloy with a change in the concentration and with a decrease of the nanocrystal size

An analytical method is proposed for calculating the properties of a disordered Au–Fe substitution alloy both with fcc and with bcc structures. The parameters of the Mie–Lennard-Jones pairwise interatomic potential for the fcc and bcc structures of Au and Fe are determined. Based on these parameters, the concentration dependences of the properties of the fcc and bcc structures of the Au–Fe alloy are calculated. It is shown that the concentration dependences are nonlinear and agree with the results obtained for fcc-Au-Fe by using density functional theory method. The changes in the lattice properties of the Au–Fe alloy under the fcc-bcc structural phase transition at a pressure of P = 0 and a temperature of T = 300 K are calculated. Based on the changes in the properties at the fcc-bcc transition, it is concluded that iron plays a major role in the phase transition in the Au–Fe alloy. The appearance of a metastable amorphous structure in a wide range of concentrations around the fcc-bcc transition in an Au–Fe alloy was explained. In the framework of the RP-model of a nanocrystal, the displacement of the iron concentration (Cf), at which the fcc-bcc phase transition occurs, due to a decrease in the nanocrystal size was calculated. It is shown that at an isochoric-isothermal decrease of the atoms number (N) in an Au–Fe nanocrystal, the Cf value increases. For a nanocrystal with a fixed of atoms number and a constant surface shape, the Cf value increases at an isochoric increase in temperature, and the Cf value decreases at an isothermal decrease in density. Calculations have shown that at N < 59 900 for the Au1–CFeC alloy at P = 0, T ≤ 300 K and at any iron concentration, the fcc structure of the nanocrystal is more stable than the bcc structure.

Global minima and structural properties of Au[sbnd]Fe nanoalloys from a Mexican Enhanced Genetic Algorithm-based Density Functional Theory

The limited mutual solubility between Au and Fe in the bulk scale has inhibited the formation of their alloys. Here we report the lowest energy structures of AuFe alloys in subnanometre scale, employing the Mexican Enhanced Genetic Algorithm coupled with density functional theory. The energetics, structural transitions, and tendency of segregation have been analysed by different stability criteria. Physico-chemical properties for all compositions have been studied using Koopman’s approximation. The topological parameters for the metal-metal interactions have been calculated using QTAIM theory. Exploring such valuable theoretical insights is of great importance in investigating new AuFe nanoalloy-based materials for technological applications.

Influence of the precipitates on the shape memory effect and superelasticity of the near–eutectoid Ti–Au–Fe alloy towards biomaterial applications

Influences of the Fe addition in various concentrations on the near–eutectoid Ti–4Au alloys were systematically investigated in this study in consideration of the great number of requirements for the biomedical materials. The Ti–4Au–xFe (x = 1, 3, 4, 5, 6, and 7 at.%) alloys were synthesized by physical metallurgy and their microstructures, crystal structures, lattice parameters, phases, and mechanical properties were analyzed. In addition, the investigations for the shape memory effect (SME) and superelasticity (SE) were also conducted to examine their performances of functionality. The β–phase was stabilized at room temperature by the 3 at.% addition of Fe into the binary Ti–4Au alloy. The specimen with optimized mechanical properties by trading–off its strength and ductility was found in the Ti–4Au–4Fe alloy. SME was revealed clearly in the Ti–4Au–3Fe alloy and slightly in the Ti–4Au–4Fe alloy; while SE was observed in the Ti–4Au–4Fe alloy. It was observed that there was a growing trend of the Ti3Au precipitate amount with the raised concentration of Fe addition. The precipitates of the Ti3Au were fine–tuned by the Fe addition for tailoring the various mechanical properties of the ternary Ti–4Au–xFe alloys, and the balanced performance was achieved by the 4 at.% Fe addition.

Изучение ГЦК-ОЦК фазового перехода в сплаве Au-Fe

The properties of the disordered Au-Fe substitution alloy are studied based on the analytical method, which uses the paired interatomic potential of Mie–Lennard-Jones. The parameters of the interatomic potential for the FCC and BCC structures of Au and Fe are determined. Based on these parameters, the concentration dependences of the properties of the FCC and BCC structures of the Au-Fe alloy are calculated. Under normal conditions (i.e., pressure P = 0 and temperature T = 300 K), changes in the properties of the Au-Fe alloy at the structural phase transition of FCC-BCC are calculated. Using the RP-model of the nanocrystal, the displacement of the Cf concentration, at which the FCC-BCC phase transition occurs, due to a decrease in the size of the nanoparticle was calculated. It is shown that at an isochoric-isothermal decrease in the number of atoms (N) in an Au-Fe nanoparticle, the Cf value displace towards higher Fe concentrations. For a nanoparticle with a fixed number of atoms and a constant surface shape, the Cf value increases at an isochoric increase in temperature, and the Cf value decreases at an isothermal decrease in density. Calculations have shown that at N &lt; 59900 for the Au1–CFeC alloy at P = 0, T &lt; 300 K and at any iron concentration, the FCC structure is more stable than the BCC structure.

On the deviation from the Vegard's law for the solid solutions

A method is proposed for calculating the lattice parameter (l) for the solid solution (i.e. disordered binary substitutional alloy), which takes into account the pressure (P) in the alloy. An analytical expression is obtained for calculating the dependence of the function l on the alloy concentration at different values of P. It is shown that for P = 0 the deviation from the Vegard's law (Δl) is due to the difference in compressibility and in specific volumes of the pure crystals. The method is approved on SiGe, CuAu and AuFe alloys, and it was showed the good agreement with the experimental data. With an isothermal increase in pressure, the value Δl increases both for alloys with a negative and for alloys with a positive deviation from the dependence obtained by the Vegard's law. Calculations showed that for the SiGe alloy, the function Δl(P) passes over to the positive region at P0 = 0.685 GPa. It was shown the thermal expansion coefficient of a solid SiGe substitution solution at P = 0 deviates in the negative direction from the dependence that follows from the Vegard's law.

Observation of exchange bias in nanoscale AuFe alloy film

We report on observation of the exchange bias effect in AuFe co-sputtered alloy films in the as-deposited state and following swift heavy ion irradiation. The Mössbauer spectrum for the as-deposited film shows a broad paramagnetic doublet together with a small contribution from hyperfine magnetic sextets. The magnetization behavior exhibits a spontaneous exchange bias effect at room temperature without application of an external triggering field. The magnitude of exchange bias in the as-deposited sample increases with decreasing temperature, at first gradually down to about 50 K and then more rapidly down to 5 K. Irradiation of AuFe film with 100 MeV Au9+ ions transforms the Mössbauer spectrum into a broad magnetic sextet, with asymmetric broadening characteristic of the formation of α-Fe magnetic nanoclusters surrounded by shells of reduced Fe concentration. At room temperature the exchange bias field is in the same sense as that for the as-deposited sample, but decreases with temperature until it reverse its sign at below about 50 K. In both the as-deposited and irradiated samples a well-defined uniaxial magnetic anisotropy, consequent on a stress induced texturing of the Fe precipitate distribution, is observed.