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Artificial modulation of a neuronal subset through ion channels activation can initiate firing patterns of an entire neural circuit in vivo. As nanovalves in the cell membrane, voltage-gated ion ch...

Magnetic nanoparticles (MNPs) have been extensively used as contrasts and tracers for bioimaging, heating sources for tumor therapy, carriers for controlled drug delivery, and labels for magnetic immunoassays. Here, we describe a MNP relaxation dynamics-based magnetic particle spectroscopy (MPS) method for the quantitative detection of molecular biomarkers. In MPS measurements, the harmonics of oscillating MNPs are recorded and used as a metric for the freedom of rotational motion, which indicates the bound states of the MNPs. These harmonics can be collected from microgram quantities of iron oxide nanoparticles within 10 seconds. Using a streptavidin-biotin binding system, we demonstrate the feasibility of using MPS to sense these molecular interactions, showing this method is able to achieve rapid, wash-free bioassays, and is suitable for future point-of-care (POC), sensitive, and versatile diagnosis., 24 pages, 8 figures, 2 schemes, 1 table

In the past 20 years, several studies have been performed on the detection of biomarkers by the stripe-shaped spin valve sensors, whose sensitivity is limited by their small sensing area and large sensor resistance. In this paper, large-area spin valve sensors with lower aspect ratio are introduced. A reverse nucleation mechanism is proposed to demonstrate the different switching processes in large-area sensors. The simulation results further prove the involvement of reverse nucleation sites during the magnetization reversal. Large-area sensors also exhibit a linear response to the concentration of magnetic nanoparticles with a sensor signal more than 20 times larger than the stripe sensors.

Superparamagnetic nanoparticles (SPMNPs), with unique physical and magnetic properties that differentiate them from their bulk magnetic materials, have been widely studied for potential applications in biomedical areas. With proper surface chemical functionalization, SPMNPs have found their applications in magnetic hyperthermia therapy, magnetic bioassays, drug delivery, magnetic manipulation, etc. These applications require elaborate tuning of the physical and magnetic properties of the SPMNPs such as saturation magnetization M s and magnetic core size D . In this work, we present a search coil-based method to directly characterize the M s of SPMNPs in the liquid phase. The nonlinear magnetic responses of SPMNPs under oscillating magnetic fields are exploited and the induced harmonic signals are used to analyze their M s and D . Different combinations of M s and D are assumed and their harmonic ratios R are summarized. Curve fitting shows that the harmonic ratio R = 0.74 + 2.85 × 10 9 ∙ D - 4.41 ∙ M s - 1.44 , with the coefficient of determination R-square = 0.98.

This work is a micromagnetic simulation-based study on the GHz-frequency ferromagnetic resonances (FMR) for the detection of magnetic nanoparticles (MNPs) using spin current nano-oscillator (SCNO) operating in precession mode. Capture antibody-antigen-detection antibody-MNP complex on the SCNO surface generates magnetic fields that modify the FMR peaks and generate measurable resonance peak shifts. Moreover, our results strongly indicate the position-sensitive behavior of the SCNO biosensor and demonstrate ways to eradicate this effect to facilitate improved bio-sensing. Additionally, a study has been made on how MNPs with different sizes can alter the SCNO device performance. This simulation-based study on the SCNO device shows the feasibility of a frequency-based nano-biosensor with the sensitivity of detecting a single MNP, even in presence of background noise.

In recent years, high-moment magnetic nanoparticles (MNPs) such as FeCo are attracting intense interest for biomedical applications. The synthesized FeCo MNPs have the specific saturation magnetization up to 226 emu/g that is more than three times higher than that of iron oxide MNPs (~ 70–80 emu/g). Core-shell MNPs are also synthesized to enhance the functionality of high-moment MNPs. Shells like SiO2, Au, and Ag are used for these high-moment MNPs to improve biocompatibility. The sputtering-based gas-phase condensation approach to synthesize high-moment MNPs and core-shell nanostructures are reviewed. The applications of these high-moment MNPs such as magnetic hyperthermia, drug delivery, magnetic resonance imaging (MRI), and biosensing are summarized. The heating efficiency of magnetic hyperthermia and drug delivery could be significantly enhanced by using high-moment MNPs. MNPs with different crystallinity and shapes (such as cubic, spherical, triangular, and octahedral shapes) are also summarized due to their potential applications in MRI. High-moment MNPs could also provide more magnetic signals for giant magnetoresistance (GMR)-based biosensors, which are also reviewed. We believe that the high-moment MNPs are promising candidates for many bio-applications.

In recent years a number of new nanotechnology based platforms have been developed for detection of wide variety of targets including infectious agents, protein biomarkers, nucleic acids, drugs, and cancer cells. Nanomaterials such as magnetic nanoparticles, quantum dots, carbon nanotubes, nanowires, and nanosensors like giant magnetoresistance (GMR) sensors are used to quantitatively detect biomolecules with, experimentally, relatively good accuracy. There has been a growing interest in the use of magnetic fields in biosensing applications. Because biological samples have no ferromagnetic property and therefore there is no interference with complex sample matrix, detection of infectious agents from minimally processed samples is possible. Here, we provide a brief overview of the recent emergence of nanotechnology-based techniques for the detection and monitoring of foodborne diseases. In addition, the potential applications and future perspectives of nanotechnology on food safety are discussed. Ultimately, the review is expected to stimulate and provide directions to the development and application of nanotechnology-based tests for the early detection, and eventual control of foodborne diseases.

Influenza A virus (IAV) is a common respiratory pathogen infecting many hosts including humans, pigs (swine influenza virus or SIV), and birds (avian influenza virus or AIV). Monitoring swine and avian influenza viruses in the wild, farms, and live poultry markets is of great significance for human and veterinary public health. A portable, sensitive, and quantitative immunoassay device will be of high demand especially in the rural and resource-limited areas. We report herein our Z-Lab point-of-care (POC) device for sensitive and specific detection of swine influenza viruses with minimum sample handling and laboratory skill requirements. In the present study, a portable and quantitative immunoassay platform based on giant magnetoresistive (GMR) technology is used for the detection of IAV nucleoprotein (NP) and purified H3N2v. Z-Lab displays quantitative results in less than 10 min with sensitivities down to 15 ng/mL and 125 TCID50/mL for IAV nucleoprotein and purified H3N2v, respectively. This platform al...

Nanomaterials, in addition to their small size, possess unique physicochemical properties that differ from bulk materials, making them ideal for a host of novel applications. Magnetic nanoparticles (MNPs) are one important class of nanomaterials that have been widely studied for their potential applications in nanomedicine. Due to the fact that MNPs can be detected and manipulated by remote magnetic fields, it opens a wide opportunity for them to be used in vivo. Nowadays, MNPs have been used for diverse applications including magnetic biosensing (diagnostics), magnetic imaging, magnetic separation, drug and gene delivery, and hyperthermia therapy, etc. Specifically, we reviewed some emerging techniques in magnetic diagnostics such as magnetoresistive (MR) and micro-Hall (μHall) biosensors, as well as the magnetic particle spectroscopy, magnetic relaxation switching and surface enhanced Raman spectroscopy (SERS)-based bioassays. Recent advances in applying MNPs as contrast agents in magnetic resonance imaging and as tracer materials in magnetic particle imaging are reviewed. In addition, the development of high magnetic moment MNPs with proper surface functionalization has progressed exponentially over the past decade. To this end, different MNP synthesis approaches and surface coating strategies are reviewed and the biocompatibility and toxicity of surface functionalized MNP nanocomposites are also discussed. Herein, we are aiming to provide a comprehensive assessment of the state-of-the-art biological and biomedical applications of MNPs. This review is not only to provide in-depth insights into the different synthesis, biofunctionalization, biosensing, imaging, and therapy methods but also to give an overview of limitations and possibilities of each technology.

Cellular-level neuron stimulation has attracted much attention in the areas of prevention, diagnosis and treatment of neurological disorders. Herein, we propose a spintronic neurostimulator based on the domain wall movement inside stationary magnetic nanowires driven by the spin transfer torque. The electromotive forces generated by the domain wall motion can serve as highly localized stimulation signals for neuron cells. Our simulation results show that the induced electric field from the domain wall motion in permalloy nanowires can reach up to 14 V/m, which is well above the reported threshold stimulation signal for clinical applications. The proposed device operates on a current range of several uA which is 10^3 times lower compared to magnetic stimulation by microcoils. The duration and amplitude of the stimulating signal can be controlled by adjusting the applied current density, the geometry of the nanowire, and the magnetic properties of the nanowire material., Comment: 11 pages, 4 figures

Magnetite ferrofluids with unique magnetic behaviors are attractive for biomedical applications such as magnetic fluid hyperthermia and magnetic particle imaging. A precise nanoparticle-specific characterization by theoretical models and experiments to predict dynamics of ferrofluids and optimize their behaviors for emerging biomedical applications is necessary. In this paper, combining experiments and modeling, we have uncovered interesting magnetic dynamics of nanoparticles that are dependent on magnetic field strength, polymer coating of nanoparticles, viscosity of ferrofluid, and dipolar interactions. It is concluded that either by changing the magnitude of magnetic field or the concentrations of nanoparticles, we are able to convert the dominating relaxation process of magnetic nanoparticles from Neel to Brownian, and vice versa. Polymer coatings on nanoparticles and viscosity of ferrofluids are demonstrated to have varying degrees of influence on effective relaxation times of nanoparticles with different sizes and under different field strengths. Our theoretical models are used to predict the magnetic response of ferrofluid consisting of 35 nm magnetite nanoparticles under alternating magnetic fields, and it turns out that our theoretical data fits well with the experimental data.