Magnetic Quantum Dots Research Articles

Interband optical absorption coefficient of the diluted magnetic semiconductor ellipsoid quantum dot with Rashba spin orbit interaction

Interband optical absorption coefficient of the diluted magnetic semiconductor ellipsoid quantum dot with Rashba spin orbit interaction

MBE growth of highly sensitive silicon PIN diode with magnetic Mn-doped Ge quantum dots for photodetector and solar cell applications

MBE growth of highly sensitive silicon PIN diode with magnetic Mn-doped Ge quantum dots for photodetector and solar cell applications

Magnetic nanoparticles and quantum dots coupled immuno nano fluorescence assay for visual detection of HPV16-induced cervical cancer cells from cytology/biopsy samples

Biopsy-based histopathology and immunohistochemistry for cervical cancer detection are costly, time-consuming, and require expert personnel for data interpretation. We developed a simple magnetic nanoparticle (MNPs) and quantum dots (QD) coupled immuno nano fluorescence assay (MNPQDCINFA) for visual detection of HPV16-induced cervical cancer cells under UV light from cytology/biopsy samples exploiting host cancer cells expressing viral E7 protein as a biomarker. The E7 domain-specific polyclonal antibodies were generated against the 1–44 amino acid N-terminal (anti-domainN antibody) and 48–98 amino acid C-terminal domain (anti-domainC antibody). These antibodies were bioconjugated with nonfluorescent MNPs (60 % efficiency) and fluorescent QDs (66 % efficiency) to generate capturing (MNPs-anti-domainN antibody) and detecting (QDs-anti-domainC antibody) nano-complex, respectively. Assay conditions, such as concentration of capturing (20 μM) and detecting (50 nM) antibody nano-complexes and incubation duration (30 min), were standardized. The analytical sensitivity using pure HPV16 E7 protein was recorded up to 200 ng with very high specificity to differentiate from other HPV strains E7 proteins. The diagnostic performance characteristics with cytology samples showed 100 % sensitivity and specificity compared to immunofluorescence and biopsy-based histopathology analysis. The present invention can be effectively used for a quick, disposable, rapid cervical cancer cell detection system as an alternate test for immunofluorescence and histopathology.

Phenylboronic Acid-Modified Membrane-Like Magnetic Quantum Dots Enable the Ultrasensitive and Broad-Spectrum Detection of Viruses by Lateral Flow Immunoassay.

Although lateral flow immunochromatographic assay (LFIA) is an effective point-of-care testing technology, it still cannot achieve broad-spectrum and ultrasensitive detection of viruses. Herein, we propose a multiplex LFIA platform using a two-dimensional graphene oxide (GO)-based magnetic fluorescent nanofilm (GF@DQD) as a multifunctional probe and 4-aminophenylboronic acid (APBA) as a broad-spectrum recognition molecule for viral glycoprotein detection. GF@DQD-APBA with enhanced magnetic/fluorescence properties and universal capture ability for multiple viruses was easily prepared through the electrostatic adsorption of one layer of density-controlled Fe3O4 nanoparticles (NPs) and thousands of small CdSe/ZnS-MPA quantum dots (QDs) on a monolayer GO sheet followed by chemical coupling with APBA on the QD surface. The GF@DQD-APBA probe enabled the universal capture and specific determination of different target viruses on the test strip through an arbitrary combination with the antibody-modified LFIA strip, thus greatly improving detection efficiency and reducing the cost and difficulty of multiplex LFIA for viruses. The proposed technique can simultaneously and sensitively diagnose three newly emerged viruses within 20 min with detection limits down to the pg/mL level. The excellent practicability of GF@DQD-APBA-LFIA was also demonstrated in the detection of 34 clinical specimens positive for SARS-CoV-2, revealing its potential for epidemic control and on-site viral detection.

Multiplex fluorescence quenching immunoassay based on multicolor magnetic quantum dot and dual spectral-overlapped polydopamine nanospheres for ultrasensitive detection of aflatoxin B1, zearalenone, ochratoxin A, and fumonisin B1

Due to the increasing fungal infections and the implementation of strict food safety regulations, the demand for sensitive, rapid, and easy assays for testing co-contaminated mycotoxins in food has grown in recent years. In this study, a multiplex fluorescence quenching immunoassay is developed to simultaneously detect prevalent mycotoxins in cereals, namely aflatoxin B1 (AFB1), zearalenone (ZEN), ochratoxin A (OTA), and fumonisin B1 (FB1). Four spherical nanocomposites with magnetic core and three-layer quantum dot (QD) shell (MagTQD) are fabricated. These nanocomposites exhibit different maximum emission peaks without overlap and interference at the same excitation wavelength. Four MagTQD conjugated with corresponding coating antigens to prepare four fluorescence signal probes with rapid magnetic enrichment ability, respectively. Moreover, polydopamine nanospheres (PDANs) with dual-spectral overlapped fluorescence quenching properties are conjugated with four mycotoxin antibodies to prepare four fluorescence quenching probes, respectively. The established immunoassay has the low detection limit at 1.29 pg mL−1 for AFB1, 0.80 pg mL−1 for ZEN, 1.97 pg mL−1 for OTA, and 13.89 pg mL−1 for FB1, respectively. This developed assay can provide a new approach to realize the efficient detection of multi-mycotoxins in food safety supervision.

Boosting energy levels in graphene magnetic quantum dots through magnetic flux and inhomogeneous gap

We study the effects of a magnetic flux and an inhomogeneous gap on the energy spectrum of graphene magnetic quantum dots (GMQDs). By considering the Dirac equation in the infinite mass framework, we can analytically obtain eigenspinor expressions. By applying boundary conditions, we obtain an energy spectrum equation in terms of system parameters such as radius, magnetic field, energy, flux, and gap. In the infinite limit, we recover Landau levels for graphene in a magnetic field. We show that the energy spectrum increases significantly in the presence of flux and a gap inside the GMQDs, which prolongs the lifetime of the trapped electron states. We show that higher flux also produces new Landau levels of negative angular momentum. Meanwhile, we find that the gap increases the separation between the electron and hole energy bands. As shown in the radial probability analysis, flux and gap emerge as influential factors in controlling electron mobility, affecting confinement, and prolonging the presence of quasi-bound states.

A CRISPR-Cas12a-powered, quantum dot-based and magnetic nanoparticle-assisted (QD-CRISPR-MNP) biosensor for the screening of Salmonella

Rapid detection methods are urgently needed to help prevent the spread of Salmonella among food products. Herein, a CRISPR-Cas12a-powered, quantum dot-based and magnetic nanoparticle-assisted (QD-CRISPR-MNP) biosensor was proposed for the screening of Salmonella. The QD-CRISPR-MNP biosensor was designed and fabricated relying on the CRISPR-Cas12a system for better guidance of the coupling between magnetic nanoparticles (MNPs) and quantum dots (QDs). In this biosensor, the activity of the CRISPR-Cas12a system was unlocked by Salmonella and displayed collateral cleavage activity towards linker DNAs, which inhibited the coupling of the MNPs and QDs. Then, Salmonella could be quantitatively detected by simply measuring the fluorescence emitted by the QDs on the MNPs surface. This biosensor showed good detection performance for Salmonella with a detection limit of 86 CFU mL−1, and exhibited a satisfactory specificity as well. Moreover, it overcomes the low fluorescence quantum yields and the possible high fluorescence background noise in conventional dye-based CRISPR detection platforms, acting as a powerful alternative for the detection of foodborne pathogens.

Carbon quantum dots-based palladium complex: A versatile nano-catalyst for the green synthesis of pyrazoles

The palladium complex based on the magnetic carbon quantum dots [Fe3O4@CQDS@Si(CH2)3 NH@CC@ATT@Pd (CQDPd = F)] was synthesized by preparation of Fe3O4, its further reactions with carbon quantum dots (CQDs), (3-aminopropyl)triethoxysilane [Si(OEt)3(CH2)3NH2], cyanuric chloride (CC), and 3-amino-1,2,4-triazole-5-thiol (ATT), and complexation of the product with PdCl2. Then, it was characterized by several techniques such as FT-IR, XRD, EDX, SEM, TEM, VSM, and used as a novel catalyst for the green synthesis of diverse pyrazoles from the reaction of aldehydes, ethyl acetoacetate and phenylhydrazine at 70 °C under solvent-free conditions with high yields and short reaction times. Aldehydes bearing the electron-withdrawing groups exhibit the superior reactivity. Remarkably, the F catalyst showed strong recyclability over six consecutive cycles with negligible loss of activity, emphasizing its sustainability and high efficiency in chemical transformations as well as the catalytic potential of the used magnetic carbon quantum dots and their ability to revolutionize green and efficient synthetic methodologies.

A Magnetic-Optical Triple-Mode Lateral Flow Immunoassay for Sensitive and Rapid Detection of Respiratory Adenovirus.

Human respiratory adenovirus (ADV) is a highly infectious respiratory virus with potential for pandemics. There are currently no specific drugs to treat ADV worldwide, so early rapid detection of ADV infection is essential. In this study, we developed an innovative magnetic-optical triple-mode lateral flow immunoassay (LFIA) using magnetic quantum dots as immunomarkers. This novel approach addresses the need for rapid and accurate ADV detection, allowing for multimodal quantitative/semiquantitative analysis of magnetic, fluorescent, and visible signals within a mere 15 min. The lower limit of detection (LOD) for magnetic, fluorescent, and visual signals was determined to be 5.6 × 103, 1.2 × 103, and 1.95 × 104 copies/mL, respectively. The detection range for ADV using this approach was 1.2 × 103-5 × 107 copies/mL. Additionally, semiquantitative analysis, which is user-friendly and does not necessitate specialized equipment, was successfully implemented. Notably, seven respiratory viruses showed no cross-reactivity with the generated LFIA test strips. The intrabatch repeatability exhibited a coefficient of variation (CV) of less than 5%, while the interbatch repeatability had a CV of less than 15%. Furthermore, recovery values ranged from 95% to 106.8% for samples analyzed concurrently with dual signals at the same spiking concentration. The assay developed in this study boasts a wide detection range and exceptional sensitivity and specificity. This technique is exceptionally well-suited for on-site rapid detection, with the potential for personal self-testing and early ADV infection diagnosis. Its versatility extends to a broad array of application scenarios.

The interplay between magnetism and structure in Co/Fe-CdSe diluted magnetic quantum dots

Revealing the structure-dependent properties of Co/Fe-CdSe DMQD. Co-ions form a β-Co(OH)2 shell, showing soft ferromagnetism and enhanced PL by 250%. Conversely, Fe-ions lead to room-temperature ferromagnetic DMQD, forming a FeSe core in the CdSe QD.

Effect of magnetic flux on scattering in a graphene magnetic quantum dot

Our theoretical investigation focuses on the impact of a magnetic flux on two aspects related to the trapping time of electrons within a graphene magnetic quantum dot (GMQD), which results from an applied magnetic field. Specifically, we examine the electron diffusion and trapping time of the quasi-states within the GMQD. Employing the Dirac equation, we derive solutions for the energy spectrum in each region comprising the GMQD, serving as mathematical tools to assess diffusion efficiency and estimate trapping time. Our findings reveal that an increase in magnetic flux enhances scattering efficiency, even in the absence of magnetic field. Through a scattering analysis in real space, we observe a significant improvement in the probability density within the GMQD. We demonstrate the feasibility of extending the trapping time of an electron within a GMQD by adjusting the magnetic flux.

Ruthenium nanoparticles encrusted with nitrogen & sulphur magnetic quantum dots as an efficient electrochemical sensor for simultaneous determination of itraconazole and terbinafine; a dual regimen for black fungus: Magnetic solid phase micro-extraction for urine and plasma analysis

After COVID-19 pandemic, Mucormycosis (black fungus) spreads as one of its related complications, due to the decrease in immunity system after administration of COVID-19 treatment drugs. A combination therapy of Itraconazole (ITR) and Terbinafine (TEB) was proved to be effective for treatment of black fungus. A novel electrochemical sensor was designed for estimation of ITR & TEB simultaneously by square wave voltammetric (SWV) technique. The sensor was fabricated using N&S-codoped magnetic quantum dots (N,S-MQDs) and ruthenium nanoparticles (Ru NPs). The fabricated sensor was characterized by cyclic voltammetry (CV), scanning electron microscope (SEM), powder X ray diffraction (pXRD), Fourier transform-Infrared (FT-IR), Raman spectroscopy and electrochemical impedance spectroscopy (EIS). Full optimization study for various experimental and instrumental parameters, in addition to method validation following International conference on Harmonization (ICH) guidelines was achieved. A good linearity in the range of 0.5–30 μg mL−1 with limit of detection (LOD) 0.24 and 0.19 μg mL−1 for ITR and TEB, respectively were obtained. The sensor was applied for analysis of ITR and TEB simultaneously in human plasma and urine samples without any interferences by applying dispersive magnetic solid phase micro-extraction (dMSPE) technique, where excellent recovery results exceeding 95 % were achieved.

Specific effects of Cr3+ dopant ions on diluted magnetic semiconductor Sb2-xCrxTe3 quantum dots in a glass matrix

Sb2-xCrxTe3 quantum dots (QDs) were synthesized in a host glass matrix through fusion and heat treatment methods. The results revealed the specific effects inherent to the doping of Cr3+ ions in diluted magnetic semiconductors (DMS) (Sb2-xCrxTe3 QDs embedded in glass matrix). Differential Thermal Analysis shows evidence of changes in glass transition and the host glass's crystallization temperatures with the presence of Sb2-xCrxTe3 QDs. Transmission electron microscopy (TEM) images and energy dispersive X-ray analysis evidenced the formation, size, and composition of these DMS QDs. The interplanar distances dhkl measured in TEM and the pattern observed in electron diffraction from the selected area reinforces the Sb2Te3 crystalline nature. Structural analyses of x-ray diffraction patterns confirm that all Sb2-xCrxTe3 QDs crystallize in the rhombohedral R3_m−D3d5 structure and that Cr3+-ions had replaced Sb3+-ions. Electronic paramagnetic resonance (EPR) spectra exhibit resonance signals confirming Cr3+ ion incorporation into the Sb2Te3 crystal lattice. Moreover, EPR shows that the sp-d exchange interactions become less pronounced with the formation of Cr3+ ─ Cr3+ pairs. Raman scattering spectroscopy confirmed the formation of Sb2-xCrxTe3 QDs. The red and blue shifts of the normal Raman- and IR-active vibrational modes characteristic of Sb2Te3 give strong evidence of the Cr3+ ion incorporation in QDs. Interestingly, the study results revealed better structural and magnetic properties. We believe that these Sb2-xCrxTe3 QDs in SNAB glass, with appropriate dopant concentration and chemical composition, are potentially efficient for thermoelectric, topological insulators, photovoltaic devices, solar cells, magnetic devices and spintronic applications.

Abstract C136: Magnetic nanoparticles and quantum dots coupled visual confirmation of cervical cancer cells from cytology samples: A cost-effective, quick and suitable test for rural Indian set-up

Abstract Introduction Screening and management of cervical cancer is a National health priority of developed and developing countries like India. Cervical cancer screening and diagnosis are currently done by cervical pap screening, colposcopy, and nucleic acid hybridization and amplification assays, which are time-consuming and require specialized facilities. These shortcomings pose severe restrictions on the feasibility of the techniques for a country like India.Aim and objectives Bearing this in mind, we aimed to develop a simple, cost-effective, and visual detection of cervical cancer, based on magnetic nanoparticles coupled quantum dots immuno-nano-fluorescence assay (MNCQDINFA).Materials and methods The detection system comprised of magnetic nanoparticles(MNP) and quantum dots (QD) conjugated specific polyclonal antibodies complex generated against recombinantly purified individual domains (domainN and domainC) of HPV-16 oncoprotein E7, which is deregulated and overexpressed to detectable limits by transformed cervical cancer cells only [1-3]. The assay procedure involves incubating processed cervical cytology samples with MNP-Ab (domainN) complex, magnet-induced pelleting, incubation with QD-Ab (domainC) complex, magnet-assisted washing, and final reconstitution in sample buffer and visualization under UV (Figure). Reconstituted sample in the presence of UV gives fluorescence as an indication of the presence of E7 protein thus cervical cancer cells. Results This method produces a visual fluorescence exclusively in the presence of transformed cervical cancer cells under UV light. Analytical assays showed that a minimum of 0.1µg of E7 protein could be detected specifically from a pool of cellular proteins. HPV 16-positive cervical cancer cell lysates showed concordant results. Both the diagnostic sensitivity and specificity of the assay were determined to be 100%. Conclusion The proposed invention is a simple, visual (naked eye), quick (4 hours), and cost-effective (INR 200-300) cervical cancer cells detection method necessary to identify the candidates at risk so that suitable and timely intervention can be provided.

Electrons trapped in graphene magnetic quantum dots with mass term

Owing to the Klein tunneling phenomenon, the permanent confinement or localization of electrons within a graphene quantum dot is unattainable. Nonetheless, a constant magnetic field can transiently ensnare an electron within the quantum dot, giving rise to what are known as “quasi-bound states” characterized by finite lifetimes. To prolong the retention of electrons within the quantum dot, we introduce a mass term into the Hamiltonian, thereby inducing an energy gap. We resolve the Dirac equation to ascertain the eigenspinors, and by ensuring their continuity at the boundaries, we investigate the scattering behavior. Our findings indicate that the presence of an energy gap can extend the lifetimes of these quasi-bound states within the quantum dot. In particular, we demonstrate that even in the absence of a magnetic field, the scattering efficiency attains significant levels when the energy gap gets closed to the incident energy of an electron traversing the quantum dot. It is found that an augmentation in the electron density within the quantum dot results in an enhancement of the electron-trapping time.

The acid modified magnetic carbon quantum dots as a capable nano-catalyst for the synthesis of pyridines and pyrazoles

The acid modified magnetic carbon quantum dots as a capable nano-catalyst for the synthesis of pyridines and pyrazoles

Te doping effects on the ferromagnetic performance of the MnGe/Si quantum dots grown by ion beam sputtering deposition

Dilute magnetic MnGe quantum dots (QDs) have been a popular research topic due to their great potential application on spintronics and their natural compatibility with today's highly developed silicon-based complementary metal oxide semiconductor (CMOS) technology. However, the relatively low Curie temperature impedes their ability to maintain the ferromagnetic phase and creates difficulty for their practical application in spintronics at room temperature. Here, we report the first preparation of the Te-doped dilute-magnetic Mn0.064Ge0.895Te0.041/Si QDs by using the ion beam composite target sputtering technique. Growth temperature and deposition thickness dependent QDs density and magnetic properties were investigated systematically. The experimental results indicate that the QD density of Mn0.064Ge0.895Te0.041/Si sample increases first and then reduces with the deposited thickness, while the QDs' diameters increase monotonously from 10.18 ± 0.21–33.6 ± 0.34 nm. Curie temperature of 369 K observed in Mn0.064Ge0.895Te0.041 QDs is higher than that of 295 K observed in Mn0.061Ge0.939 counterparts grown at the same conditions. Correspondingly, the saturation and residual magnetization in the former are much higher than in the latter. The ferromagnetic enhancement can be attributed to that the nonpolar Mn0.064Ge0.936 QDs transform into Rashba polar Mn0.064Ge0.895Te0.041 QDs with the doping of Te ions, which obviously promotes the exchange coupling between holes and Mn atoms. Our work provides a practical approach for improving the ferromagnetism and Curie temperature of silicon-based diluted magnetic semiconductor QDs.

Soft ferromagnetic effect in FePc/CdS hybrid diluted magnetic organic/inorganic quantum dots

Manipulating magnetic interactions in diluted magnetic quantum dots (DMQDs) is a fundamental research field due to the potential for developing robust magnetic semiconducting materials that can operate effectively in various environmental conditions. Here we design a new class of DMQDs via hybridization of inorganic CdS QDs with organic iron phthalocyanine (FePc) molecules. By a combination of X-ray photoemission, Mӧssbauer spectroscopies, and vibrating sample magnetometry, we demonstrate that FePc molecules alter the original diamagnetic nature of CdS QDs. They turn them into room-temperature soft-ferromagnets, while preserving the CdS QD structure from further oxidation in a more efficient way than the standard Fe doping of CdS QDs. These hybrid materials open up new possibilities for the design of DMQDs of tunable and robust magnetism for optomagnetic and spintronic applications.

Spin-dependent resonant Andreev tunneling in hybrid ferromagnetic metal–magnetic quantum dot–superconductor nanostructures

There exists a variety of theoretical proposals to transform states induced by magnetic nanoparticles inside a superconducting gap into Majorana fermion states. The main challenge in this route is a conclusive proof and undoubted distinguishing between topologically trivial subgap Andreev bound states and topologically nontrivial magnetically polarized Majorana bound states. This motivated us to investigate a nonequilibrium electrons tunneling through a ferromagnetic normal metal–magnetic quantum dot–s-wave superconductor (F-mQD-SC) nanostructure, where the mQD’s discrete levels are spin splitted. By using the Keldysh Green’s function method, the expressions for a tunnel current and probability of the Andreev reflection (AR) versus energy are derived and studied. We find that the system’s resonant ARs conductance exhibits different kinds of peaks depending on a spin splitting of the mQD levels, the spin polarization magnitude of the F-lead current, the gate voltage, and an external magnetic field magnitude. The nanostructure’s conductance versus a bias voltage exhibits extra peaks which at some combination of its parameters can mimic ones expected for Majorana modes in a topological superconducting state. The distinguishing transport characteristics of a F-mQD-SC nanoscale structure being in non-topological state are discussed. We suggest that the results obtained can provide helpful clarification for understanding recent experiments in superconductor–ferromagnet hybrid nanostructures with topologically protected excitations.

A Novel Approach to Design Multiplexer Using Magnetic Quantum-Dot Cellular Automata

Magnetic quantum-dot cellular automata (MQCA) is a recent technology in computation based on closely coupled ferromagnetic and antiferromagnetic dots; it is favorable as the fabrication issues arise day by day at the nanometer scale in CMOS technology. In this letter, first, we propose MQCA-based 2:1 Multiplexer using conventional horizontal and vertical approaches. In the next step, we propose a novel area efficient compact design approach with the help of the explicit interaction, coupling concept & dominant nature of slant edge nanomagnets. The proposed compact design methodology leads to 71%-97% reduction in the total number of nanodots and 22%-99% reduction in area occupancy compared to the horizontal, vertical, nanomagnetic QCA, and existing QCA-based 2:1 Mux. To showcase the scalability of our proposed structure, we also implement an 8:1 Multiplexer. The design layouts and simulation results are verified using the MuMax3 micromagnetic simulator.