Magnetic Dots Research Articles

Effect of inhomogeneous gap on energy levels in graphene magnetic quantum dots

We study the energy levels of fermions magnetically confined in graphene through an electrostatic potential and an inhomogeneous gap, including Δ2 inside and Δ1 outside of the generated quantum dots. Our findings illustrate that the energy levels exhibit either symmetric or asymmetric behavior, contingent upon the signs of τ and the quantum angular momentum number m. It is discovered that Δ1 acts by breaking the symmetry and generating a new set of energies.

Emergent Magnetic Field and Nonzero Gyrovector of the Toroidal Magnetic Hopfion

Magnetic hopfions are localized magnetic solitons with a nonzero 3D topological charge (Hopf index). Herein, an analytical calculation of the magnetic hopfion gyrovector is presented and it is shown that it does not vanish even in an infinite sample. The calculation method is based on the concept of the emergent magnetic field. The particular case of the simplest nontrivial toroidal hopfion with the Hopf index in the cylindrical magnetic dot is considered and dependencies of the gyrovector components on the dot sizes are calculated. Nonzero hopfion gyrovector is important in any description of the hopfion dynamics within the collective coordinate Thiele's approach.

Controllable synthesis of bifunctional magnetic carbon dots for rapid fluorescent detection and reversible removal of Hg2+

Mercury is one of the most toxic heavy metals, whose identification and separation are crucial for environmental remediation. Till now, it remains a significant challenge upon simultaneous detection and removal of Hg2+. Herein, bifunctional probe magnetic carbon dots were synthesized and optimized via systematic structure manipulation of the carbon and iron precursors towards fluorescence, Hg2+ adsorption and magnetic separation. The probe exhibited blue emission at 440 nm with high quantum yield of 55 % and a high paramagnetism with the saturation magnetization value of 22.70 emu/g. Furthermore, the fluorescent detection of Hg2+ with limit of 5.40 nM and high selectivity were achieved through surface structure manipulation with moderate -NH2, -SH and Fe contents. As a result, the magnetic removal of Hg2+ was consecutively effectuated with high removal efficiency of 98.30 %. The detection and recovery of Hg2+ in real samples were further verified and demonstrated the excellent environmental tolerance of probe. The reusability was viable with recycling at least three turns by external magnet. This work not only provides a promising approach for simultaneous detection and removal of heavy metal pollution, but also provides an excellent example as a versatile platform for multifunction integration via the structure manipulation for other applications.

Magnetic quantum dots barcodes using Fe3O4/TiO2 with weak spectral absorption in the visible region for high-sensitivity multiplex detection of tumor markers

Magnetic quantum dot (QD) barcode holds great potential for automatic suspension array and rapid point-of-care detection since it enables simultaneous target encoding, enrichment and separation. However, a serious obstacle to enhancing the encoding capacity of magnetic QD microbeads (MBs) is the fluorescence quenching of magnetic nanoparticles (MNPs) to quantum dots (QDs) in the visible wavelength range due to the broad and strong optical absorption spectrum of MNPs. Here, we report Fe3O4/TiO2 core/shell MNPs and CdSe/ZnS QDs for the construction of dual-function magnetic QD barcodes. Fe3O4/TiO2 MNPs can significantly inhibit fluorescence quenching because the weak absorption of visible light by the TiO2. The two-dimension barcode library of 30 magnetic QD barcodes was constructed based on Fe3O4/TiO2 MNPs and CdSe/ZnS QDs. Moreover, the magnetic QD barcodes showed high sensitivity for the multiplex detection of four tumor markers, cancer antigen 125 (CA125), cancer antigen 199 (CA199), alpha-fetoprotein (AFP), and neuron specific enolase (NSE) with detection limits of 0.89 KU/L, 0.72 KU/L, 0.05 ng/mL, and 0.15 ng/mL, respectively. This bifunctional magnetic QD barcodes are promising for automatic high-sensitivity multiplex bioassay.

Hydrogen bonding donor/acceptor active sites exposed on imide-functionalized carbon dots aid in enhancing arsenic adsorption performance

During the arsenic (As) adsorption process, amino-functionalization has been widely considered as one of the effective adsorbents optimization methods, while this study reveals that imide functional groups also play a non-negligible role. Herein, magnetic carbon dots (CDs) equipped with imide (FeCD-NH) or amino functional groups (FeCD-NH2) were synthesized to deduce the relationship between different configurations of amino-like functional groups and As. The results showed that FeCD-NH exhibited extraordinary As(V) adsorption behavior (with 97.80 % As(V) removal within 5 min), outperformed that equipped with amino functional groups (FeCD-NH2). An array of advanced characterization techniques and density functional theory (DFT) calculation collectively revealed a dual-configuration hydrogen bond synergistic mechanism of FeCD-NH toward As(V). Different from monomorphic hydrogen bond of amino functional group, imide functional group forms abundant adsorption sites through dual-configuration hydrogen bonds to realize the ultrafast adsorption of As(V). In addition, FeCD-NH can remove As(V) from other more complex water matrices to levels below the World Health Organization (WHO) drinking water standards and the Chinese surface water standards. Therefore, this work provides a promising strategy for As decontamination by fine-tune the surface chemistry of adsorbents.

Graphene quantum dots-based magnetic relaxation switch involving magnetic separation for enhanced performances of endoglin detection using ultra-low-field nuclear magnetic resonance relaxometry

Magnetic relaxation switches (MRS) based on target-induced state changes of magnetic nanoparticles are vital approaches for biomolecule detection in in vitro diagnosis. Recently, magnetic graphene quantum dots have been employed as magnetic probes instead of iron oxide nanoparticles and showed high sensitivity. Introducing magnetic separation into an MRS assay before the relaxometry measurements can enhance the sensitivity, elevate accuracy, and expand the linear region. In this work, magnetic separation-assisted MRS was developed to detect endoglin utilizing iron oxide as the magnetic carrier and magnetic graphene quantum dots as the magnetic probe. The assay possesses a broad linear region from 5 ng/mL to 50 μg/mL and a sensitive limit of detection of 1.3 ng/mL, which is two orders of magnitude lower than that of MRS without magnetic separation. The high accuracy and consistency have been proved for endoglin (CD105) detection in real samples. This graphene quantum dot-based MRS involving magnetic separation provides a new route for enhancing the sensitivity and accuracy of biomolecule detection.

Ultra-broadband microwave absorption of honeycomb-like three-dimensional carbon foams embedded with zero-dimensional magnetic quantum dots

The magnetic response behavior of microwave absorbing materials (MAMs) is beneficial to the expansion of the effective bandwidth in the high-frequency electromagnetic fields. However, the high density of magnetic components does not match with the lightweight requirement of MAMs. In response to this contradiction, the metal-organic framework (MOF) ZIF-67 material and melamine foam were used in the present work as the magnetic component and self-sacrificial template, respectively. A three-dimensional honeycomb carbon foam with zero-dimensional magnetic Co quantum dots (Co-QDs/CF) was prepared by a simple two-step method. The unique honeycomb structure significantly improved impedance matching and carrier mobility, providing more scattering paths for the electromagnetic wave conduction while reducing the overall density. In turn, the uniformly embedded magnetic Co-QDs endowed the 3D carbon foam with excellent high-frequency magnetic response while ensuring light weight. The ultra-small size (<10 nm) enhanced the exchange coupling between magnetic particles while suppressing the eddy current effect, and the magnetic loss capability was greatly improved. Interestingly, Co-QDs acting as numerous micro-resistors formed a large three-dimensional conductive network with the carbon skeleton, which demonstrated outstanding electron transport ability, so that the conductance loss was significantly enhanced. Surprisingly, the effective absorption bandwidth of Co-QDs/CF in the 2–18 GHz band was as high as 8.74 GHz with a matching thickness of 2.5 mm, while the corresponding filling rate was only 20 wt%. Thus, the proposed ingenious strategy to construct three-dimensional conductive networks using ultra-small magnetic quantum dots opens up new prospects for the development of lightweight broadband MAMs.

Smart pH-responsive magnetic graphene quantum dots nanocarriers for anticancer drug delivery of curcumin

In this study, we designed a targeted multifunctional anticancer drug carrier based on magnetic to improve the efficiency of curcumin (Cur) as a non-toxic and hydrophobic anticancer medicine. Graphene quantum dots (GQDs) were synthesized from graphene oxide (GO), and then magnetic nanocomposite was prepared with chemical co-precipitation of Fe2+ and Fe3+. As a cancer-targeting agent, folic acid (FA) was conjugated and named GQDs-Fe3O4-FA nanocomposite. FTIR, VSM, XRD, and FE-SEM analyses were used to characterize the as-synthesized nanocomposite. Fourier transformed infrared (FTIR) results revealed that GQDs-Fe3O4 was synthesized, and FA was attached to it. Furthermore, according to the VSM analysis, it can be seen that GQDs-Fe3O4 has superparamagnetic behavior (Ms = 60.6 emu/g), which is shown that an applied magnetic field can steer it to the cancerous tumor site without damaging the healthy tissues. The cumulative release behavior of the drug (Cur) was monitored in phosphate buffered saline (PBS, pH 5.5 and 7.4) for 150 h. It was observed that 33% and 15% of total curcumin were released at pH 5.5 and 7.5, respectively. In vitro cytotoxicity of GQDs-Fe3O4 and Cur/GQDs-Fe3O4-FA were investigated against MCF-7 and MG-63 cells by the MTT-Assay test. According to an in vitro cytotoxicity assay, these cell lines are more vulnerable to Cur/GQDs-Fe3O4-FA than Cur/GQDs-Fe3O4, which revealed the selective role of folic acid as a targeting agent in nanocarriers. The results also showed nontoxicity of the bare nanocarrier on normal cells. Therefore, GQDs-Fe3O4-FA can be a potential and compelling candidate for therapeutic applications, including drug delivery systems.

Magnetic MoS2 efficient heterogeneous photocatalyst for the α-methoxymethylation and aminomethylation of aromatic ketones

Magnetic MoS2 quantum dots are designed and applied as an efficient photocatalyst for the α-methoxymethylation and aminomethylation of aromatic ketones using methanol as a green C1 source in air under visible-light irradiation at room temperature.

Effect of an Array of Submicron Magnetic Dots on Magnetization, Critical Current, and the Structure of Vortex Configurations in HTS

Effect of an Array of Submicron Magnetic Dots on Magnetization, Critical Current, and the Structure of Vortex Configurations in HTS

Влияние массива субмикронных магнитных точек на намагниченность, критический ток и структуру вихревых конфигураций в ВТСП

A vortex lattice in a high-temperature superconductor (HTS) with an array of submicron magnetic dots on the surface has been studied by the Monte Carlo method within the framework of a three-dimensional model of a layered high-temperature superconductor. The adjustment of the vortex lattice to an array of magnetic points was observed — ordered states arising in the process of remagnetization — configurations of one, two, three, or more vortex filaments fixed to a single magnetic point. The occurrence of these configurations was accompanied by peaks on the magnetization curve. The influence of the HTS anisotropy on the adjustment of the vortex lattice is analyzed. The ordered configurations of the vortex lattice are also associated with the non-monotonic nature of the dependences of the superconductor critical current on the magnetic field. The influence of temperature, magnetic moment of points, and film thickness on the critical current is investigated. With an increase in temperature and a decrease in the magnetization of magnetic points, the maximum of the critical current shifts towards a lower field. The structure of vortex filaments in the inhomogeneous field of a magnetic point is analyzed in detail. The mechanism of the influence of ordered vortex configurations on magnetization and critical current is discussed.

Long-Range Magnetic Order in Nickel Hydroxide-Functionalized Graphene Quantum Dots.

In this work, we demonstrate the prospect of chemically synthesizing transition metal (Ni) doped magnetic graphene quantum dots (GQDs) with the sole aim of shedding light on their magnetic properties. Our results show that adsorption of nickel hydroxide on predominantly paramagnetic GQDs reveals antiferromagnetic ordering in the M-T profile around 10 K with change of the spin exchange coupling deviating from J = 1/2 to J = 1, mainly arising from the d-p mixing hybridization between the p orbital of carbon from the GQD and the d orbital of Ni. Furthermore, our results are well complemented by ab initio simulations showing asymmetry of the up and down spins around the Fermi level for nickel hydroxide-doped GQDs with long-range spin polarization. Furthermore, the magnitude of the net magnetic moment generated for doped GQDs on the carbon atoms is found to be site-dependent (surface or edge).

Synthesis of magnetic graphene quantum dots based molecularly imprinted polymers for fluorescent determination of quercetin

In this work, modified magnetic graphene quantum dots with molecularly imprinted polymer coating (Fe3O4@GQDs/MIP) through the self-assembly reaction of APTES (functional monomer), TEOS (cross-linker) and quercetin (template) molecules as a low-cost new green adsorbent with high selectivity and sensitivity for easy evaluation of quercetin medicinal compound using the quenching effect of quercetin on the fluorescence emission intensity of graphene quantum dots (GQDs) were synthesized. The morphology and composition of GQDs, magnetic graphene quantum dots (Fe3O4@GQDs) and Fe3O4@GQDs/MIP by Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDAX) techniques were determined. The regular and uniform distribution of spherical nanoparticles of Fe3O4@GQDs/MIP was well observed by SEM imagings. In the next part of this project, the effective parameters in the process of measuring quercetin such as concentration of adsorbent, pH and contact time were investigated, that the optimal values of concentration of adsorbent 0.6 mg mL−1, pH 8.0 and contact time 10 min were obtained. In the optimized conditions, quercetin with a linear range of 5–220 ng mL−1 with detection limit of 0.54 ng mL−1 and recoveries of 97.61–102.11(%) and repeatability of 1.18–3.71(%) in real samples of green tea, cumin and thyme was successfully measured and detected.

Ultrasensitive Fluorescence Lateral Flow Assay for Simultaneous Detection of Pseudomonas aeruginosa and Salmonella typhimurium via Wheat Germ Agglutinin-Functionalized Magnetic Quantum Dot Nanoprobe.

Point-of-care testing methods for the rapid and sensitive screening of pathogenic bacteria are urgently needed because of the high number of outbreaks of microbial infections and foodborne diseases. In this study, we developed a highly sensitive and multiplex lateral flow assay (LFA) for the simultaneous detection of Pseudomonas aeruginosa and Salmonella typhimurium in complex samples by using wheat germ agglutinin (WGA)-modified magnetic quantum dots (Mag@QDs) as a universal detection nanoprobe. The Mag@QDs-WGA tag with a 200 nm Fe3O4 core and multiple QD-formed shell was introduced into the LFA biosensor for the universal capture of the two target bacteria and provided the dual amplification effect of fluorescence enhancement and magnetic enrichment for ultra-sensitivity detection. Meanwhile, two antibacterial antibodies were separately sprayed onto the two test lines of the LFA strip to ensure the specific identification of P. aeruginosa and S. typhimurium through one test. The proposed LFA exhibited excellent analytical performance, including high capture rate (&gt;80%) to the target pathogens, low detection limit (&lt;30 cells/mL), short testing time (&lt;35 min), and good reproducibility (relative standard deviation &lt; 10.4%). Given these merits, the Mag@QDs-WGA-based LFA has a great potential for the on-site and real-time diagnosis of bacterial samples.

Degradation of ciprofloxacin by green cobalt oxide quantum dots

Ciprofloxacin (CIPRO) is a fluoroquinolone antibiotic extensively used to treat various bacterial infections. The extensive use of CIPRO has promoted its accumulation in diverse aquatic environments as an emergent pollutant. Concentrations of CIPRO found in surface and ground waters and sea vary from ng to mg/L and represent a real risk for the rise of new resistant bacterial strains. The complex and stable chemical CIPRO structure is not favorable for biological degradation. However, magnetic Co3O4 quantum dots (Co3O4 QDs) with 5 nm of mean diameter synthesized using biomolecules from tomato (Solanum lycopersicum L.) seed extract were efficient in promoting photodegradation of this emergent pollutant under UV irradiation. UV–visible and Fourier Transform Infrared (FTIR) spectrophotometry corroborated CIPRO degradation. The photodegradation using UV light in the presence of Co3O4 QDs was the more efficient strategy to impair the bactericidal action of CIPRO and, consequently, avoid the development of bacteria-resistant strains. The Co3O4 QDs are a low-cost, efficient, and green option for CIPRO degradation.

Preparation and characterization of Rutin loaded on magnetic graphene quantum dot nano career with metals (Ag, Zn, Mg, Co, and Fe) and study of antioxidant and electrochemical properties

Rutin, is one of the flavonoids, and has high antioxidant properties, but is limited due to low solubility in aqueous solutions. To increase the antioxidant performance and permeability, the synthesis of magnetic graphene quantum dot metal nanocomposites and the antioxidant activity of the prepared nanocomposites have been studied. Rutin was treated with metal magnetic nanocomposites, GQD-MFe2O4, that included metals like Silver, Magnesium, Zinc, Cobalt, and Iron. The metal nanocomposites reacted with Rutin to obtain Rutin-bearing magnetic nanocomposites. The GQD-MFe2O4 nanocomposites were synthesized by common hydrothermal pyrolysis of citric acid and subsequent the addition of iron nitrate and metal nitrate (M= Ag, Mg, Co, Zn, Fe) to the media. The scavenging test of free radical activity and DPPH test of prepared nanomagnetic composites show good antioxidant activity. The results show that the derivatives of magnetic nanocomposites have different antioxidant activities compared to Rutin as ordered: GQD-ZnFe2O4-Ru<GQD-CoFe2O4-Ru<Rutin<AGQD-MgFe2O4-Ru<GQD-Fe3O4-Ru<GQD-AgFe2O4-Ru.The structure and morphology of magnetic graphene quantum dots metal composites and related Rutin loaded nanocomposites have been tested and proved by Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Energy Dispersive X-Ray (EDX), Differential Scanning Calorimetry (DSC), UV-Visible, and Cyclic Voltammetry (CV) techniques. The morphology of nanocomposites shows particles less than 60 nm. The CV plot of nanocomposites represents the quasi-reversible performance of the nanocomposites. The results show that the derivatives of magnetic nanocomposites have different antioxidant activities compared to Rutin.

Optical properties of cylindrical quantum dots with diluted magnetic semiconductors structure

The optical properties of diluted magnetic semiconductor cylindrical quantum dot caused by interband transitions are investigated. The behavior of a quantum dot as a function of the energy of an incident photon is studied for various values of temperature, magnetic field, and structural parameters. It is shown that a change in the distance between the energies of electrons and holes in identical quantum states affects the maximum of the absorption coefficient. According to the results obtained, an increase in temperature increases the absorption maximum and shifts it toward lower energy. As the magnetic field increases, the absorption maximum decreases and shifts toward higher energy. In addition, it was found that the absorption threshold frequency varies linearly at high temperatures and nonlinearly at low temperatures depending on the magnetic field.

Caustical patterns in circular magnetic dots in graphene

Caustical patterns in circular magnetic dots in graphene

Field-Free Superconducting Diode in a Magnetically Nanostructured Superconductor

A strong superconducting diode effect (SDE) is revealed in a thin superconducting film periodically nanostructured with magnetic dots. The SDE is caused by the current-activated dissipation mitigated by vortex-antivortex pairs (VAPs), which periodically nucleate under the dots, move and annihilate in the superconductor - eventually driving the system to the high-resistive state. Inversing the polarity of the applied current destimulates the nucleation of VAPs, the system remains superconducting up to far larger currents, leading to the pronounced diodic response. Our dissipative Ginzburg-Landau simulations detail the involved processes, and provide reliable geometric and parametric ranges for the experimental realization of such a non-volatile superconducting diode, which operates in absence of any applied magnetic field while being fluxonic by design.

Unraveling the physical properties of Mn-doped CdS diluted magnetic semiconductor quantum dots for potential application in quantum spintronics

Unraveling the physical properties of Mn-doped CdS diluted magnetic semiconductor quantum dots for potential application in quantum spintronics