Magnetic Quantum Dots Research Articles

Nanomaterials towards Biosensing of Alzheimer's Disease Biomarkers.

Alzheimer’s disease (AD) is an incurable and highly debilitating condition characterized by the progressive degeneration and/or death of nerve cells, which leads to manifestation of disabilities in cognitive functioning. In recent years, the development of biosensors for determination of AD’s main biomarkers has made remarkable progress, particularly based on the tremendous advances in nanoscience and nanotechnology. The unique and outstanding properties of nanomaterials (such as graphene, carbon nanotubes, gold, silver and magnetic nanoparticles, polymers and quantum dots) have been contributing to enhance the electrochemical and optical behavior of transducers while offering a suitable matrix for the immobilization of biological recognition elements. Therefore, optical and electrochemical immuno- and DNA-biosensors with higher sensitivity, selectivity and longer stability have been reported. Nevertheless, strategies based on the detection of multiple analytes still need to be improved, as they will play a crucial role in minimizing misdiagnosis. This review aims to provide insights into the conjugation of nanomaterials with different transducers highlighting their crucial role in the construction of biosensors for detection of AD main biomarkers.

Extraction of trace amounts of cadmium in fish and mollusk by Fe3O4@N-carbon quantum dots as adsorbent

The extraction of trace amounts of cadmium ions in fish and mollusk was investigated using magnetic N-doped carbon quantum dots as adsorbent. The characterization of the adsorbent was performed using Fourier transform infrared spectroscopy, UV–Vis spectroscopy, X-ray diffraction spectrometry, vibrating sample magnetometer and transmission electron microscopy. Important parameters, with effective role on extraction process were optimized in three levels by central composite design. The parameters including extraction time (5, 35, 65 min), amount of the magnetic sorbent (10, 30, 50 mg) and pH (3, 5, 7) were recognized as the major factors in adsorption process and optimized. The variables including type (HCl, HNO3, HCl/thiourea, HNO3/thiourea), volume (1, 3, 5 mL) and concentration of desorption solvent (0.01, 0.5, 1 mol L−1), and desorption time (1, 5.5, 10 min) were optimized in desorption process. Under the optimum conditions (pH of 6.30; extraction time of 5 min; adsorbent amount of 10 mg; desorption solvent volume of 1.5 mL; desorption time of 5 min; desorption solvent concentration of 0.5 mol L−1), the adsorption capacity was 246 mg g−1. The detection (S/N = 3) and quantitation limits of the method were found to be 0.06 and 0.2 μg L−1, respectively. The method was also successfully used for the determination of Cd2+ in fish and mollusk samples with satisfactory recoveries (≥ 97.4%).

Magnetic CoFe alloy@C nanocomposites derived from ZnCo-MOF for electromagnetic wave absorption

Magnetic quantum dot (QD)-like CoFe alloy@C nanocomposites derived from ZnCo-MOF using low-dimensional carbon as carriers for electromagnetic wave (EMW) absorption were successfully synthesized by in situ growth and pyrolysis. The resulting CoFe@C nanocomposites were homogeneously conjoined with different carbon supports such as two-dimensional (2D) reduced graphene oxide (rGO) and one-dimensional (1D) carbon nanotubes (CNT). Results indicated EMW absorption properties of CoFe@C were enhanced by introduction of rGO and CNT as carbon hosts for the construction of conductive networks due to the excellent impedance matching and electromagnetic attenuation. The rGO-supported CoFe@C composites annealed at 900 °C (rGO-CoFe@C-900) revealed a minimum reflection loss (RLmin) of −36.08 dB at the sample thickness of 3.0 mm and an effective bandwidth (RL < −10 dB) of 5.17 GHz at 3.5 m. Moreover, the CNT-supported CoFe@C nanocomposites pyrolyzed at 900 °C (CNT-CoFe@C-900) exhibited optimum EMW absorption performances due to the continuous 3D conductive networks, RLmin of −40.00 dB with the thickness of 3.0 mm, and effective absorption bandwidth reached 5.62 GHz with a thickness of 2.0 mm. In particular, the specific reflection loss values of the resulting nanocomposites significantly preceded that of the reported similar dielectric-magnetic hybrids. In view of the superior EMW absorption properties, the as-fabricated low-dimensional carbon-supported magnetic quantum dot-like (QD-like) CoFe alloy@C composites will be utilized as ideal candidates for high-efficient EMW absorption.

Magnetic quantum dot based lateral flow assay biosensor for multiplex and sensitive detection of protein toxins in food samples

Protein toxins, such as botulinum neurotoxin type A (BoNT/A) and staphylococcal enterotoxin B (SEB), easily pollute food and water and are ultra-toxic to humans and animals, thus requiring a sensitive on-site detection method. In this study, we reported a novel lateral flow assay (LFA) strip on the basis of magnetic quantum dot nanoparticles (MagQD NPs) for sensitive and multiplex protein toxin detection in food samples. A new type of MagQD NP was prepared by fixing the dense carboxylated QDs on the surface of polyethyleneimine-modified Fe3O4 magnetic NPs (MNPs) and applied in LFA with the following functions: capture and enrich target toxins from sample solutions and serve as advanced fluorescent labels for the quantitative determination of targets on the strip. Through this strategy, the assay realized quantified BoNT/A and SEB detection in 30 min with the limits of detection of 2.52 and 2.86 pg/mL, respectively. The selectivity and the ability of quantitative analysis of the method were validated in real food samples, including milk and juice. This MagQD-LFA biosensor showed considerable potential as a point-of-care testing tool for the sensitive detection of trace toxins.

Supraparticle Assemblies of Magnetic Nanoparticles and Quantum Dots for Selective Cell Isolation and Counting on a Smartphone-Based Imaging Platform.

There are numerous diagnostic and therapeutic applications for the detection and enumeration of specific cell types. Flow cytometry is the gold standard technique for this purpose but is poorly suited to point-of-need assays. The ideal platform for these assays would combine the immunocytochemical capabilities of flow cytometry with low-cost, portable instrumentation, and a simple and rapid assay workflow. Here, we present a smartphone-based imaging platform (SIP) in tandem with magnetic-fluorescent suprananoparticle assemblies as a step toward these ideal criteria. The assemblies (MNP@QD) are magnetic iron oxide nanoparticles surrounded by a dense corona of many brightly luminescent semiconductor quantum dots (QDs), where both the assemblies and their immunoconjugates are prepared by self-assembly. As proof of concept, we show that the MNP@QD and SIP pairing is able to selectively isolate, fluorescently immunolabel, and count breast cancer cells that are positive for human epidermal growth factor receptor 2 (HER2). These results are an important foundation for future point-of-need diagnostics capable of multiplexed isolation, counting, and immunoprofiling of cells on a smartphone, enabled by the highly advantageous optical properties of QDs.

Splitting of conductance resonance through a magnetic quantum dot in graphene

We report a dual resonance feature in ballistic conductance through a quantum Hall graphene nanoribbon with a magnetic quantum dot. Such a magnetic quantum dot localizes Dirac fermions exhibiting anisotropic eigenenergy spectra with broken time-reversal symmetry. Interplay between the localized states and quantum Hall edge states is found to be two-fold, showing Breit-Wigner and Fano resonances, which is reminiscent of a double quantum dot system. By fitting the numerical results with the Fano-Breit-Wigner lineshape from the double quantum dot model, we demonstrate that the two-fold resonance is due to the valley mixing that comes from the coupling of the magnetic quantum dot with quantum Hall edge channels; an effective double quantum dot system emerges from a single magnetic quantum dot in virtue of the valley degree of freedom. It is further confirmed that the coupling is weaker for the Fano resonance and stronger for the Breit-Wigner resonace.

Magnetic Fluorescence Molecularly Imprinted Polymer Based on FeOx/ZnS Nanocomposites for Highly Selective Sensing of Bisphenol A.

In this study, magnetic fluorescence molecularly imprinted polymers were fabricated and used for the selective separation and fluorescence sensing of trace bisphenol A (BPA) in environmental water samples. The carboxyl-functionalized FeOx magnetic nanoparticles were conjugated with mercaptoethylamine-capped Mn2+ doped ZnS quantum dots to prepare magnetic FeOx and ZnS quantum dot nanoparticles (FeOx/ZnS NPs). Additionally, molecular imprinting on the FeOx/ZnS NPs was employed to synthesize core-shell molecularly imprinted polymers. The resulting nanoparticles were well characterized using transmission electron microscopy, Fourier transform infrared spectra, vibrating sample magnetometer and fluorescence spectra, and the adsorption behavior was investigated. Binding experiments showed that the molecularly imprinted FeOX/ZnS NPs (FeOx/ZnS@MIPs) exhibited rapid fluorescent and magnetic responses, and high selectivity and sensitivity for the detection of bisphenol A (BPA). The maximum adsorption capacity of FeOx/ZnS@MIPs was 50.92 mg·g−1 with an imprinting factor of 11.19. Under optimal conditions, the constructed fluorescence magnetic molecularly imprinted polymers presented good linearity from 0 to 80 ng mL−1 with a detection limit of 0.3626 ng mL−1 for BPA. Moreover, the proposed fluorescence magnetic polymers were successfully applied to on-site magnetic separation and real-time fluorescence analysis of target molecule in real samples.

Fabrication of magnetic quantum dots modified Z-scheme Bi2O4/g-C3N4 photocatalysts with superior hydroxyl radical productivity for the degradation of rhodamine B

The kernel of photocatalytic technology is to exploit photocatalytic materials with high efficiency, stability and easy recovery. Herein, we designedly prepare a magnetic quantum dot (Fe3O4 QDs) as co-catalyst to modify Z-scheme Bi2O4/g-C3N4 (Bi/CN) composite photocatalyst via combining calcination with hydrothermal method. The morphology, chemical composition and physicochemical properties of photocatalysts are systematically analyzed by a series of characterization means. The experimental results explicitly render that the optimum Fe3O4-QDs/Bi2O4/g-C3N4 (FeQDs/Bi/CN) has outstanding photocatalytic performance than that of Bi2O4, g-C3N4 and Bi2O4/g-C3N4 (Bi/CN), which is chiefly imputed to the synergistic effect of Z-scheme heterojunction system and Fenton reaction. The Z-scheme heterojunction is conductive to accelerate charge carrier separation and makes electrons and holes retain higher redox ability. Fe3O4 QDs can promote visible light absorption and generate more hydroxyl active (OH) substances through Fenton reaction. Furthermore, the magnetic photocatalyst is liable to separate under the action of external magnetic field, which ensures that is convenient for industrial application. The mechanism of photocatalytic degradation is discussed in detail by capturing experiments, ESR and liquid fluorescence detection. This work unveils more possibilities for modifying Z-scheme heterojunction system to improve photocatalytic performance.

Pd@magnetic Carbon Dot Immobilized on the Cyclodextrin Nanosponges ‐ Biochar Hybrid as an Efficient Hydrogenation Catalyst

AbstractWith the aim of benefiting from the advantage of magnetic catalysts, chemistry of cyclodextrin, i. e. the capability of formation of inclusion complex and acting as phase transferring agent, as well as biochars as biocompatible, cost‐effective and efficient catalyst support, for the first time a ternary hybrid system composed of cyclodextrin nanosponges (CDNS), palladated magnetic carbon quantum dot (Pd@CQDs@Fe) and Bell‐pepper‐derived biochar (Biochar) was designed and prepared through functionalization of CDNS and Biochar and their covalent conjugation followed by immobilization of Pd@CQDs@Fe. The hybrid system was characterized and then applied as a magnetic heterogeneous catalyst for promoting hydrogenation of nitroarenes. The results confirmed high catalytic activity, selectivity and recyclability of the catalyst (up to ten reaction runs) as well as low Pd leaching. Comparing the catalytic activity of the catalyst with some control samples, the contribution of CDNS, Biochar and CQDs@Fe to the catalysis was confirmed.

High density sulfonated magnetic carbon quantum dots as a photo enhanced, photo-induced proton generation, and photo switchable solid acid catalyst for room temperature one-pot reaction

The preparation of photo enhanced and switchable (on/off mode) sulfonated magnetic carbon quantum dots was investigated in the present work. First, the as-synthesized carbon quantum dots (CQDs) were easily separated using a magnet (instead of using a dialysis method), then CQDs decorated with high density (9.6 mmol/g) acid groups (sulfonic + carboxylic) using chlorosulfonic acid. The photo-switchable activity of the catalyst related to the photoexitation of charge separation which in turn leads to electron withdrawing property in sulfonic groups. On the other hand, it was shown that sulfonated magnetic carbon quantum dot (S-M-CQDs) is more efficient than magnetic carbon quantum dot (M-CQDs). The as-prepared catalyst was characterized using SEM, TEM, EDX, XRD, IR, VSM and TGA. The catalytic activity of the as-prepared catalyst was evaluated at room temperature in one-pot reaction (synthesis of hexahydroquinoline derivatives). The as-synthesized catalyst easily retrieved using a magnet (than ultracentrifugation) and used in the next cycles.

Multifunctional magneto-fluorescent NiZnFe@CdS core-shell nanostructures for multimodal applications

Magneto-fluorescent nanostructures are promising materials for application in biological fields such as optically tracked targeted drug delivery systems etc, and in the field of electronics and spintronics. Here, a new set of magneto-fluorescent core-shell nanostructures were formed from the Ni-Zn-ferrite as magnetic core and CdS quantum dots as fluorescent semiconducting shell with exceptional physical and chemical properties of individual magnetic core and QDs shell. These magneto-fluorescent nanostructures were prepared to overcome the limitations present in the studied iron oxide based magneto-fluorescent or magneto-plasmon nanostructures in the field. These magneto-fluorescent nanostructures were prepared using two-step process, which includes sol-gel and wet chemical methods. Ni-Zn-ferrites@CdS nanostructures were synthesized for different loadings of ferrite with different sizes of CdS QDs, where 2-mercaptoethanol was used as the stabilizing agent for the controlled growth of CdS QDs size. Ni-Zn ferrites, CdS and core-shell Ni-Zn-ferrite@CdS nanoparticles were investigated for structural, optical and magnetic properties. X-ray studies reveal the structural properties of Ni-Zn ferrite, CdS QDs, and Ni-Zn-ferrite@CdS. The optical properties of prepared nanoparticles were characterized by UV–visible and photoluminescence spectroscopy at room temperature. High-resolution transmission electron microscopy was used to observe the core-shell structure. Vibrating sample magnetometer was used to study the magnetic behavior of the samples at room temperature.

Microfluidic continuous flow synthesis of functional hollow spherical silica with hierarchical sponge-like large porous shell

Microfluidics brings unique opportunities for engineering micro-/nanomaterials with well-controlled physicochemical properties. Herein, using a miniaturized multi-run spiral-shaped microreactor, we develop a flow synthesis strategy to continuously produce hollow spherical silica (HSS) with hierarchical sponge-like pore sizes ranging from several nanometers to over one hundred nanometers. The formation of HSS is realized by mixing two reactant flows, one containing cetyltrimethylammonium bromide (CTAB) and diluted ammonia and the other 1,3,5-trimethylbenzene (TMB) and diluted tetraethyl orthosilicate (TEOS), at a flow rate as high as 5 mL/min. The effect of the reactant concentration and the flow rate on the structural change of the resultant materials is examined. Functional small-sized nanoparticles (magnetic nanoparticle, quantum dot, and silver nanoparticle) can be separately assembled into HSS and high molecular weight protein (bovine serum albumin) can be successfully loaded into HSS and delivered into cancer cells afterward, making them promising in the fields of separation and purification, bioimaging, catalysis, and theranostics.

Aggregation-induced enhanced photoluminescence in magnetic graphene oxide quantum dots as a fluorescence probe for As(iii) sensing

Magnetic graphene quantum dots have been designed for sensing arsenic in contaminated water based on aggregation induced photoluminescence phenomenon.

Enrichment and Identification of Fetal Nucleated Red Blood Cells from Maternal Blood with Magnetic Nanoparticles and Quantum Dots

Enrichment and Identification of Fetal Nucleated Red Blood Cells from Maternal Blood with Magnetic Nanoparticles and Quantum Dots

Fluorescent hybrid nanospheres induced by single-stranded DNA and magnetic carbon quantum dots

Assembled DNA nanospheres were preparedviaself-assembly with magnetic CQDGd as the building blocks and negatively charged ssDNA as the assembly units.

Helical spin thermoelectrics controlled by a side-coupled magnetic quantum dot in the quantum spin Hall state

We study the thermoelectric response of a device containing a pair of helical edge states contacted at the same temperature $T$ and chemical potential $\mu$ and connected to an external reservoir, with different chemical potential and temperature, through a side quantum dot. Different operational modes can be induced by applying a magnetic field $B$ and a gate voltage $V_g$ at the quantum dot. At finite $B$, the quantum dot acts simultaneously as a charge and a spin filter. Charge and spin currents are induced, not only through the quantum dot, but also along the edge states. We focus on linear response and analyze the regimes, which we identify as charge heat engines or refrigerator, spin heat engine and spin refrigerator.

Superparamagnetic graphene quantum dot as a dual-modality contrast agent for confocal fluorescence microscopy and magnetomotive optical coherence tomography.

A magnetic graphene quantum dot (MGQD) nanoparticle, synthesized by hydrothermally reducing and cutting graphene oxide-iron oxide sheet, was demonstrated to possess the capabilities of simultaneous confocal fluorescence and magnetomotive optical coherence tomography (MMOCT) imaging. This MGQD shows low toxicity, significant tunable blue fluorescence and superparamagnetism, which can thus be used as a dual-modality contrast agent for confocal fluorescence microscopy (CFM) and MMOCT. The feasibility of applying MGQD as a tracer of cells is shown by imaging and visualizing MGQD labeled cells using CFM and our in-house MMOCT. Since MMOCT and CFM can offer anatomical structure and intracellular details, respectively, the MGQD for cell tracking could provide a more comprehensive diagnosis.

The Role of Magnetic Quantum Dot Cellular Automata In Replacing Traditional CMOS Technology

The Role of Magnetic Quantum Dot Cellular Automata In Replacing Traditional CMOS Technology

Microwave Assisted Phytosynthesis and Characterization of Magnetic Iron Oxide Quantum Dots using Moringa oleifera

Magnetic Iron Oxide Quantum Dots (MIOQDs) were synthesized using Moringa oleifera leaves through green technique i.e., Microwave treatment. The synthetic method is highly rapid, simple and economical. MIOQDs were formed by reduction of ferric chloride (FeCl3) solution with Moringa oleifera leaf extract without any influence of alkaline conditions which opens a new arena for the phytosynthesis of nanoparticles. MIOQDs structural characteristics were scrutinized by Powder X-ray diffraction method, FESEM, TEM, UV –Visible Spectroscopy, Photoluminescence Emission Spectroscopy. The ultraviolet-visible spectrum recorded for the aqueous media iron nanoparticles showed an absorption peak at around 330 nm. Powder X-ray diffraction showed that the particles are crystalline in nature, with both hematite and maghemite structure.

Confinement of Dirac electrons in graphene magnetic quantum dots

We characterize the confinement of massless Dirac electrons under axially symmetric magnetic fields in graphene, including zero energy modes and higher energy levels. In particular, we analyze in detail the Aharonov–Casher theorem, on the existence of zero modes produced by magnetic fields with finite flux in two dimensions. We apply techniques of supersymmetric quantum mechanics to determine the confined states by means of the quantum number j associated to isospin and angular momentum. We focus on magnetic fields, regular at the origin, whose asymptotic behaviour is , with α a real number. A confinement of infinite zero-energy modes and excited states is possible as long as . When the quantum dot is able to trap an infinite number of zero modes but no excited states, while for only a finite number of zero modes are confined.