The influence of growth temperature Ts (300-773 K) on the structural phase ordering, static and dynamic magnetization behaviour has been investigated in ion beam sputtered full Heusler alloy Co2FeAl ...(CFA) thin films on industrially important Si(100) substrate. The B2 type magnetic ordering is established in these films based on the clear observation of the (200) diffraction peak. These ion beam sputtered CFA films possess very small surface roughness of the order of subatomic dimensions (<3 Å) as determined from the fitting of XRR spectra and also by AFM imaging. This is supported by the occurrence of distinct Kiessig fringes spanning over the whole scanning range (~4°) in the x-ray reflectivity (XRR) spectra. The Gilbert damping constant α and effective magnetization 4πMeff are found to vary from 0.0053 ± 0.0002 to 0.0015 ± 0.0001 and 13.45 ± 00.03 kG to 14.03 ± 0.04 kG, respectively. These Co2FeAl films possess saturation magnetization ranging from 4.82 ± 0.09 to 5.22 ± 0.10 μB/f.u. consistent with the bulk L21-type ordering. A record low α-value of 0.0015 is obtained for Co2FeAl films deposited on Si substrate at Ts ~ 573 K.
A detailed understanding of the different mechanisms being responsible for terahertz (THz) emission in ferromagnetic (FM) materials will aid in designing efficient THz emitters. In this report, we ...present direct evidence of THz emission from single layer CoFormula: see textFeFormula: see textBFormula: see text (CoFeB) FM thin films. The dominant mechanism being responsible for the THz emission is the anomalous Hall effect (AHE), which is an effect of a net backflow current in the FM layer created by the spin polarized current reflected at the interfaces of the FM layer. The THz emission from the AHE-based CoFeB emitter is optimized by varying its thickness, orientation, and pump fluence of the laser beam. Results from electrical transport measurements show that skew scattering of charge carriers is responsible for the THz emission in the CoFeB AHE-based THz emitter.
Yttrium doping-stabilized γ-Fe
2
O
3
nanoparticles were studied for its potential to serve as a plant fertilizer and, through enzymatic activity, support drought stress management. Levels of both ...hydrogen peroxide and lipid peroxidation, after drought, were reduced when γ-Fe
2
O
3
nanoparticles were delivered by irrigation in a nutrient solution to
Brassica napus
plants grown in soil. Hydrogen peroxide was reduced from 151 to 83 μM g
−1
compared to control, and the malondialdehyde formation was reduced from 36 to 26 mM g
−1
. Growth rate of leaves was enhanced from 33 to 50% growth compared to fully fertilized plants and SPAD-measurements of chlorophyll increased from 47 to 52 suggesting improved agronomic properties by use of γ-Fe
2
O
3
nanoparticles as fertilizer as compared to chelated iron.
We present an electrical sensor that uses rolling circle amplification (RCA) of DNA to stretch across the gap between two electrodes, interact with metal nanoparticle seeds to generate an ...electrically conductive nanowire, and produce electrical signals upon detection of specific target DNA sequences. RCA is a highly specific molecular detection mechanism based on DNA probe circularization. With this technique, long single-stranded DNA with simple repetitive sequences are produced. Here we show that stretched RCA products can be metalized using silver or gold solutions to form metal wires. Upon metallization, the resistance drops from TΩ to kΩ for silver and to Ω for gold. Metallization is seeded by gold nanoparticles aligned along the single-stranded DNA product through hybridization of functionalized oligonucleotides. We show that combining RCA with electrical DNA detection produces results in readout with very high signal-to-noise ratio, an essential feature for sensitive and specific detection assays. Finally, we demonstrate detection of 10 ng of Escherichia coli genomic DNA using the sensor concept.
Because of the serological cross-reactivity among the flaviviruses, molecular detection methods, such as reverse-transcription polymerase chain reaction (RT-PCR), play an important role in the recent ...Zika outbreak. However, due to the limited sensitivity, the detection window of RT-PCR for Zika viremia is only about one week after symptom onset. By combining loop-mediated isothermal amplification (LAMP) and AC susceptometry, we demonstrate a rapid and homogeneous detection system for the Zika virus oligonucleotide. Streptavidin-magnetic nanoparticles (streptavidin-MNPs) are premixed with LAMP reagents including the analyte and biotinylated primers, and their hydrodynamic volumes are dramatically increased after a successful LAMP reaction. Analyzed by a portable AC susceptometer, the changes of the hydrodynamic volume are probed as Brownian relaxation frequency shifts, which can be used to quantify the Zika virus oligonucleotide. The proposed detection system can recognize 1 aM synthetic Zika virus oligonucleotide in 20% serum with a total assay time of 27min, which can hopefully widen the detection window for Zika viremia and is therefore promising in worldwide Zika fever control.
•Synthetic Zika virus oligonucleotide is quantified by an AC susceptometer.•Amplicons of the LAMP reaction are attached to the magnetic nanoparticles.•Mg2P2O7 deposits onto the nanoparticles and further improves the signal.•An LOD of 1 aM oligos can be achieved with a total assay time of 27min.
Superstructural assembly of magnetic nanoparticles enables approaches to biosensing by combining specially tailored properties of superstructures and the particular advantages associated with a ...magnetic or optomagnetic read-out such as low background signal, easy manipulation, cost-efficiency, and potential for bioresponsive multiplexing. Herein, we demonstrate a sensitive and rapid miRNA detection method based on optomagnetic read-out, duplex-specific nuclease (DSN)-assisted target recycling, and the use of multilayer core-satellite magnetic superstructures. Triggered by the presence of target miRNA and DSN-assisted target recycling, the core-satellite magnetic superstructures release their “satellites” to the suspension, which subsequently can be quantified accurately in a low-cost and user-friendly optomagnetic setup. Target miRNAs are preserved in the cleaving reaction and can thereby trigger more cleavage and release of “satellites”. For singleplex detection of let-7b, a linear detection range between 10 fM and 10 nM was observed, and a detection limit of 4.8 fM was obtained within a total assay time of 70 min. Multiplexing was achieved by releasing nanoparticles of different sizes in the presence of different miRNAs. The proposed method also has the advantages of single-nucleotide mismatch discrimination and the ability of quantification in a clinical sample matrix, thus holding great promise for miRNA routine multiplex diagnostics.
•CFA films grown by ion-beam sputtering at room temperature on MgO(100) followed by post-annealing at 300°C and 400 °C.•XRD analysis revealed that the CFA grows with preferred crystallographic ...orientation.•Dominancy of cubic anisotropy is confirmed by the analysis of MOKE, and is quantified by employing FMR.•Presence of a combination of domain walls such as 90°, 135° and 180° domain walls and/or complex domains is supported by micromagnetic simulations.
Co2FeAl (CFA) thin films of 50 nm thickness have been grown on MgO (0 0 1) single crystal substrates at room temperature with and without post-annealing (PA) at 300 °C and 400 °C using dual ion-beam sputtering technique. The XRD pattern of the as-grown film revealed that CFA grows with preferred crystallographic orientation on the MgO (0 0 1) substrate. Temperature dependent anisotropy measurements on PA films revealed a dominating contribution from cubic anisotropy as confirmed by the analysis of azimuthal angle dependent longitudinal in-plane magneto-optical Kerr effect (MOKE) measurements. The contributions from the cubic and uniaxial anisotropies have also been quantified employing ferromagnetic resonance spectroscopy. Magnetization reversal is accompanied with a plateau in the MOKE hysteresis recorded at various azimuthal angles in the in-plane applied magnetic field configuration. The occurrence of the observed plateau is explained by the presence of a combination of domain walls such as 90°, 135° and 180° domain walls and/or complex domains which is supported by results from micromagnetic simulations. These results demonstrate the feasibility of manipulating the magnetization switching in one of the two ferromagnetic electrodes of the magnetic tunnel junction devices based on Heusler alloy ferromagnetic films.
There is an increasing need to develop biosensor methods that are highly sensitive and that can be combined with low-cost consumables. The use of magnetic nanoparticles (MNPs) is attractive because ...their detection is compatible with low-cost disposables and because application of a magnetic field can be used to accelerate assay kinetics. We present the first study and comparison of the performance of magnetic susceptibility measurements and a newly proposed optomagnetic method. For the comparison we use the C-reactive protein (CRP) induced agglutination of identical samples of 100nm MNPs conjugated with CRP antibodies. Both methods detect agglutination as a shift to lower frequencies in measurements of the dynamics in response to an applied oscillating magnetic field. The magnetic susceptibility method probes the magnetic response whereas the optomagnetic technique probes the modulation of laser light transmitted through the sample. The two techniques provided highly correlated results upon agglutination when they measure the decrease of the signal from the individual MNPs (turn-off detection strategy), whereas the techniques provided different results, strongly depending on the read-out frequency, when detecting the signal due to MNP agglomerates (turn-on detection strategy). These observations are considered to be caused by differences in the volume-dependence of the magnetic and optical signals from agglomerates. The highest signal from agglomerates was found in the optomagnetic signal at low frequencies.
•We present a direct comparison of AC susceptibility and optomagnetic CRP detection.•The techniques probe different properties of a suspension of magnetic nanoparticles.•A turn-off detection strategy gives the same results using the two techniques.•A turn-on detection strategy gives different results due to size dependent signals.•Optomagnetic readout is most sensitive to aggregation using the phase of the signal.
A turn-on competitive immunoassay using a low-cost Blu-ray optomagnetic setup and two differently sized magnetic particles (micron-sized particles acting as capture particles and nano-sized particles ...acting as detection particles) is here presented. For Salmonella detection, a limit of detection of 8×104CFU/mL is achieved within a total assay time of 3h. The combination of a competitive strategy and an optomagnetic setup not only enables a turn-on read-out format, but also results in a sensitivity limit about a factor of 20 times lower than of volumetric magnetic stray field detection device based immunoassays. The improvement of sensitivity is enabled by the formation of immuno-magnetic aggregates providing steric hindrance protecting the interior binding sites from interaction with the magnetic nanoparticle labels. The formation of immuno-magnetic aggregates is confirmed by fluorescence microscopy. The system exhibits no visible cross-reaction with other common pathogenic bacteria, even at concentrations as high as 107CFU/mL. Furthermore, we present results when using the setup for a qualitative and homogeneous biplex immunoassay of Escherichia coli and Salmonella typhimurium.
•A Blu-ray optomagnetic based immunoassay for detection of Salmonella is described.•A limit of detection of 8×104CFU/mL is achieved within a total assay time of 3h.•The formation of immuno-magnetic aggregates is studied by fluorescence microscopy.•Competitive and direct immunoassay formats are compared.•A qualitative and homogeneous biplex immunoassay is demonstrated.
The transition metal dichalcogenides have instigated a lot of interest as harmonic generators due to their exceptional nonlinear optical properties. Here, the molybdenum disulfide (MoS2) molecular ...structures with dopants being in a plasma state are used to demonstrate the generation of intense high-order harmonics. The MoS2 nanoflakes and nickel-doped MoS2 nanoflakes produced stronger harmonics with higher cut-offs compared with Mo bulk and MoS2 bulk. Conversely, the MoS2 with nickel nanoparticles and carbon nanotubes (MoS2-NiCNT) produced weaker coherent XUV emissions than other materials, which is attributed to the influence of phase mismatch. The influence of heating and driving pulse intensities on the harmonic yield and cut-off energies are investigated in MoS2 molecular structures. The enhanced coherent extreme ultraviolet emission at ~32 nm (38 eV) due to the 4p-4d resonant transitions is obtained from all aforementioned molecular structures, except for MoS2-NiCNT.
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