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.

Magnetite nanoparticles coated with citric acid are not phytotoxic and stimulate soybean and alfalfa growth.

In this work, the internalization and distribution of citric acid-coated magnetite nanoparticles (here, Fe3O4-NPs) in soybean and alfalfa tissues and their effects on plant growth were studied. Both legumes were germinated in pots containing an inert growing matrix (vermiculite) to which Hoagland solution without (control, C), with Fe3O4-NPs (50 and 100 mgironL-1, NP50 and NP100), or with the same amount of soluble iron supplied as Fe-EDTA (Fe50, Fe100) was added once before sowing. Then, plants were watered with the standard nutrient solution. The observation of superparamagnetic signals in root tissues at harvest (26 days after emergence) indicated Fe3O4-NPs uptake by both legumes. A weak superparamagnetic signal was also present in the stems and leaves of alfalfa plants. These findings suggest that Fe3O4-NPs are readily absorbed but not translocated (soybean) or scarcely translocated (alfalfa) from the roots to the shoots. The addition of both iron sources resulted in increased root weight; however, only the addition of Fe3O4-NPs resulted in significantly higher root surface; shoot weight also increased significantly. As a general trend, chlorophyll content enhanced in plants grown in vermiculite supplemented with extra iron at pre-sowing; the greatest increase was observed with NP50. The only antioxidant enzyme significantly affected by our treatments was catalase, whose activity increased in the roots and shoots of both species exposed to Fe3O4-NPs. However, no symptoms of oxidative stress, such as increased lipid peroxidation or reactive oxygen species accumulation, were evidenced in any of these legumes. Besides, no evidence of cell membrane damage or cell death was found. Our results suggest that citric acid-coated Fe3O4-NPs are not toxic to soybean and alfalfa; instead, they behave as plant growth stimulators.

Biocompatible Iron-Boron Nanoparticles Designed for Neutron Capture Therapy Guided by Magnetic Resonance Imaging.

The combination of multiple functions in a single nanoparticle (NP) represents a key advantage of nanomedicine compared to traditional medical approaches. This is well represented by radiotherapy in which the dose of ionizing radiation should be calibrated on sensitizers biodistribution. Ideally, this is possible when the drug acts both as radiation enhancer and imaging contrast agent. Here, an easy, one-step, laser-assisted synthetic procedure is used to generate iron-boron (Fe-B) NPs featuring the set of functions required to assist neutron capture therapy (NCT) with magnetic resonance imaging. The Fe-B NPs exceed by three orders of magnitude the payload of boron isotopes contained in clinical sensitizers. The Fe-B NPs have magnetic properties of interest also for magnetophoretic accumulation in tissues and magnetic hyperthermia to assist drug permeation in tissues. Besides, Fe-B NPs are biocompatible and undergo slow degradation in the lysosomal environment that facilitates in vivo clearance through the liver-spleen-kidneys pathway. Overall, the Fe-B NPs represent a new promising tool for future exploitation in magnetic resonance imaging-guided boron NCT at higher levels of efficacy and tolerability.

Facile synthesis by laser ablation in liquid of nonequilibrium cobalt-silver nanoparticles with magnetic and plasmonic properties.

Appealing physical and chemical properties are foreseen in nanoparticles containing immiscible elements, despite their synthesis is challenging due to the unfavorable thermodynamics. Here we show that silver nanoparticles doped with Co can be achieved by a facile one-step route relying on laser ablation in liquid. Structural analysis suggests that the bimetallic nanoparticles consist of a matrix of face-centred cubic Ag rich of cobalt as point defects or dislocations, in a structure that is stable over time even in aqueous solution. This happens despite the complete immiscibility of the two metals at any temperature in the solid and liquid phase, as confirmed also by density functional theory calculations. The nonequilibrium Co-Ag nanoparticles benefit of silver features such as the plasmonic response and the easy surface chemistry with thiolated ligands, combined with the magnetic properties of cobalt. Importantly, plasmonics and magnetism are not quenched after mixing, contrary to what was observed in other bimetallic systems like the Au-Fe one. This opens the way to several technologically relevant applications and, as a proof of concept, we demonstrate magnetophoretic assembly of Co-Ag nanoparticles into arrays of plasmonic dots exploitable for surface-enhanced Raman spectroscopy.

Multitherapy magnetic theranostic: Synthesis, characterization and in vitro evaluation of their performance.

It is well known that iron oxide magnetic nanoparticles (IONPs) have many potential utilities in biomedicine due to their unique physicochemical properties. With the aim to obtain multifunctional nanoparticles with potential uses for therapy and diagnosis (nanotheranostics), IONPs were synthesized by hydrothermal synthesis assisted by mannose. Two synthetic pathways were evaluated in order to obtain IONPs with suitable properties for biomedical applications. The formulation Mag@Man/H1 presented the best characteristics in terms of size and stability. Mag@Man/H1 was evaluated as: a) drug carrier, b) antioxidant activity, c) magnetic hyperthermia, d) contrast agent for MRI. To evaluate the point a), morin, a natural flavonoid with several pharmaceutical activities, was loaded on the nanoparticles. A high percentage of drug loading was achieved. In point b) it was determined that the carrier itself possess a high activity which increased in morin loaded nanoparticles. Point c) magnetocalorimetric evaluation were carried out at several field conditions. A specific absorption rate value of 121.4 W/gFe was achieved at 52.4 kA/m and 260 kHz and 8.8 W/gFe at 4 kA/m and 100 kHz. Regarding contrast capacity (point d), the r1 value found was close to some contrast agent based on manganese. Although the measured r2 value was quite smaller than other iron oxides, the achieved effect was strong enough to produce negative contrast. From these studies, it was concluded that Mag@Man/H1 could act as a multifunctional nanoplatform for oncological diseases treatments.

4D Multimodal Nanomedicines Made of Nonequilibrium Au-Fe Alloy Nanoparticles.

Several examples of nanosized therapeutic and imaging agents have been proposed to date, yet for most of them there is a low chance of clinical translation due to long-term in vivo retention and toxicity risks. The realization of nanoagents that can be removed from the body after use remains thus a great challenge. Here, we demonstrate that nonequilibrium gold-iron alloys behave as shape-morphing nanocrystals with the properties of self-degradable multifunctional nanomedicines. DFT calculations combined with mixing enthalpy-weighted alloying simulations predict that Au-Fe solid solutions can exhibit self-degradation in an aqueous environment if the Fe content exceeds a threshold that depends upon element topology in the nanocrystals. Exploiting a laser-assisted synthesis route, we experimentally confirm that nonequilibrium Au-Fe nanoalloys have a 4D behavior, that is, the ability to change shape, size, and structure over time, becoming ultrasmall Au-rich nanocrystals. In vivo tests show the potential of these transformable Au-Fe nanoalloys as efficient multimodal contrast agents for magnetic resonance imaging and computed X-ray absorption tomography and further demonstrate their self-degradation over time, with a significant reduction of long-term accumulation in the body, when compared to benchmark gold or iron oxide contrast agents. Hence, Au-Fe alloy nanoparticles exhibiting 4D behavior can respond to the need for safe and degradable inorganic multifunctional nanomedicines required in clinical translation.

Selective contrast agents with potential to the earlier detection of tumors: Insights on synthetic pathways, physicochemical properties and performance in MRI assays.

Magnetic iron oxide nanoparticles (MNPs) have been prepared and stabilized with three organic acids (tartaric, malic and ascorbic) in order to obtain biocompatible and water dispersible MNPs with potential to bind specifically to tumoral cancer cells. An in deep characterization was performed aiming to verify the presence and effect of the coating and stabilizer on MNPs surface. Besides the mechanisms followed by the different acids to bind MNPs were elucidated and used to justify the differences in the physicochemical properties of each formulation. Data related to characterization revealed that MNPs coated with ascorbic acid (MNPs-AA) resulted the most suitable in terms of their size, surface charge and stability along the time. Besides, ascorbic acid may be recognized by GLUTs receptors that are overexpressed in several kinds of tumoral cells. Therefore, MNPs-AA was selected to explore its performance in both MRI and in vitro assays using human colon cancer cells HCT 116. MRI experiments were performed in clinical equipment using a series of aqueous dispersions of MNPs-AA that were evaluated as T2 contrast agent. The T2- weighted images obtained as well as the calculated r2, indicated that MNPs-AA could act as efficient T2 contrast agent for MRI. Regarding in vitro assays, MNPs-AA did not alter the cellular function neither exert cytotoxicity using the three explored doses. The internalization of the nanoparticles on the cellular structure was confirmed quanti and qualitatively using atomic absorption spectroscopy and Prussian blue techniques respectively. From these results, it emerges that ascorbic acid coated-magnetite nanoparticles may be used as alternative contrast agent to avoid or minimize some toxicological issues related to the widely used gadolinium.

Hybrid nanomaterials based on gum Arabic and magnetite for hyperthermia treatments.

In this study, one-step co-precipitation method was conveniently adapted to obtain novel nanomaterials based on Gum Arabic and magnetite. Two synthesis procedures were evaluated: one employing the solid biopolymer in the co-precipitation media; a second using an aqueous solution of the polysaccharide. An exhaustive characterization of both formulations was performed using several specific techniques. The obtained data confirmed the successful incorporation of the gum Arabic on the magnetic core. Values of hydrodynamic diameters, measured by dynamic light scattering, in aqueous dispersions were about 70-80nm, while sizes lower than 20nm were registered by TEM microscopy. Surface charge of gum Arabic coated magnetic nanoparticles was significantly different from the corresponding to raw materials (magnetite and GA). This fact confirmed the formation of hybrid nanosystems with novel and specific properties. The potential utility of these materials was tested regarding to magnetic hyperthermia therapy under radiofrequency fields. Magnetocalorimetric measurements were performed in a wide range of field amplitude and frequency. Specific absorption rate of 218W/gFe was determined at field frequency of 260kHz and amplitude of 52kA/m. These results demonstrate their viability to be applied in tumor ablation treatments. Using the linear response theory and restricting field parameters to the accepted biomedical window, maximum useful value of 74w/gFe is predicted at 417kHz and 12kA/m.

Optical and Magnetic Properties of Fe Nanoparticles Fabricated by Femtosecond Laser Ablation in Organic and Inorganic Solvents.

Magnetic nanoparticles have attracted much interest due to their broad applications in biomedicine and pollutant remediation. In this work, the optical, magnetic, and structural characteristics of colloids produced by ultrashort pulsed laser ablation of a solid Fe target were studied in four different media: HPLC water, an aqueous solution of trisodium citrate, acetone, and ethanol. Optical extinction spectroscopy revealed an absorption band in the UV region for all, in contrast to the results obtained with nanosecond lasers. Micro-Raman spectroscopy showed that the samples are heterogeneous in their composition, with hematite, maghemite, and magnetite nanoparticles in all four solvents. Similar results were obtained by electron diffraction, which also found α-Fe. Magnetic properties were studied by vibrating-sample magnetometry, and showed nanoparticles in the superparamagnetic state. Under certain experimental conditions, submicrometer-sized iron oxide nanoparticles agglomerate into fractal patterns that show self-similar properties. Self-assembled annular structures on the nanometer scale were also observed and are reported for the first time.

Magnetically Assembled SERS Substrates Composed of Iron-Silver Nanoparticles Obtained by Laser Ablation in Liquid.

The widespread application of surface-enhanced Raman scattering (SERS) would benefit from simple and scalable self-assembly procedures for the realization of plasmonic arrays with a high density of electromagnetic hot-spots. To this aim, the exploitation of iron-doped silver nanoparticles (NPs) synthesized by laser ablation of a bulk bimetallic iron-silver target immersed in ethanol is described. The use of laser ablation in liquid is key to achieving bimetallic NPs in one step with a clean surface available for functionalization with the desired thiolated molecules. These iron-silver NPs show SERS performances, a ready response to external magnetic fields and complete flexibility in surface coating. All these characteristics were used for the magnetic assembly of plasmonic arrays which served as SERS substrates for the identification of molecules of analytical interest. The magnetic assembly of NPs allowed a 28-fold increase in the SERS signal of analytes compared to not-assembled NPs. The versatility of substrate preparation and the SERS performances were investigated as a function of NPs surface coating among different thiolated ligands. These results show a simple procedure to obtain magnetically assembled regenerable plasmonic arrays for repeated SERS investigation of different samples, and it can be of inspiration for the realization of other self-assembled and reconfigurable magnetic-plasmonic devices.