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Microwave-assisted (MWA) technique has been used in the syntheses area as it has many advantages over the conventional routes. Optimization of one-pot synthesis of ferrofluid was conducted using domestic 2.45 GHz microwave (MW). The nanoparticles were synthesized in an aqueous solution of FeCl3.6H2O as precursor and NH3 as nucleating agent. Although there are a number of reports on the MWA iron oxide nanoparticle synthesis, a quantitative optimization study on the process is still lacking. Here, MW parameters were manipulated in order to optimize the synthesis. The optimization was designed and statistically analyzed using face-centered central composite design software. The optimized conditions for MWA synthesis of ferrofluid were 80 °C reaction temperature, 14 min reaction time at 300 W producing 0.338 g of magnetic nanoparticles. Based on the characteristic studies done on synthesized ferrofluid by using X-ray diffraction, field emission scanning electron microscope, antitransmit receive (ATR) Fourier-transform infrared spectroscopy, and vibrating sample magnetometer, the nanoparticles possessed the same structure as the standard maghemite with good magnetic properties. The process produces ferrofluid of high purity with an average crystallite size of ~15 nm. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the influence of the size distribution of magnetic nanoparticles (MNPs) on the magnetic signal and mathematical model of ac magnetic nanothermometry (MNTM). Based on the Taylor expansion of the Langevin function, two novel and real-time temperature estimation models that consider the size distribution of MNPs are proposed. These models use the summation and ratio of odd-harmonic amplitudes of signal induced by MNPs in the differential pick-up coil, respectively. The simulation results show that there is a large difference between the harmonic amplitudes of monosized and multisized MNPs. The experiments are performed under low-frequency (117 Hz) and weak (30 Oe) sinusoidal ac magnetic field. Therefore, the influence of magnetic relaxations and truncation error on MNTM can be ignored. Experimental results show that the maximum temperature estimation error of model I is about 0.63 K with a standard deviation of 0.21 K, whereas that of model II is about 0.60 K with a standard deviation of 0.32 K in the measurement time of 1 s. In addition, the problem of relative temperature sensitivity and noise for these two models are discussed. [ABSTRACT FROM AUTHOR]

Aggregation of \beta -amyloid ( \text{A}\beta ) is one of the early events in Alzheimer’s disease (AD) pathology and is considered to initiate the amyloid cascade. It is presumed that \text{A}\beta plaque might coexist with biogenic magnetite. In order to understand the combined effect and mechanism of the biogenic magnetite and \textA\beta in AD, it is necessary to clarify the role of the magnetite in \textA\beta aggregation. Due to the magnetic characteristic of the magnetite, it possibly mediates the effect of environmental magnetic field (MF) on \textA\beta aggregation. Here, we preliminarily characterized the morphology of \textA\beta 40 aggregation coincubated with a magnetic nanoparticle coated with SiO2 (MNP-SiO2) in the presence of an external extremely low-frequency MF (ELF MF) exposure. Coincubation with MNP-SiO2 accelerated \textA\beta 40 aggregation and MF exposure led to more heterogeneous \textA\beta species. The results indicated that the exposure of ELF MF and MNP-SiO2 could alter the \textA\beta 40 aggregation. It will provide insights to understand the roles of ELF MF exposure and biogenic magnetite in the AD pathology. [ABSTRACT FROM AUTHOR]

Magnetic hyperthermia using magnetic nanoparticles (MNPs) draws significant interest for application in heat therapy for cancerous tumors, wherein it is important to improve the heating efficiency, i.e., to increase the hysteresis loss. In this paper, we examined the hysteresis loss of magnetically fractionated MNPs for hyperthermia application. Original Resovist MNPs were magnetically fractionated into three types, and their hysteresis loops were measured with an excitation field of 2.5 mT (rms) at a frequency of 20 kHz. The hysteresis loss of fractionated MNPs with the larger magnetic moment was approximately two times that of the original Resovist MNPs. A numerical simulation based on the Langevin function was performed to support the experimental results. From the experimental and simulation results, we can conclude that the efficiency of hyperthermia is improved by magnetically separating MNPs. [ABSTRACT FROM AUTHOR]

This paper reports on a new system of magnetic nanoparticle spectrometer to measure the magnetization spectrum of a magnetic nanoparticle based sample induced in alternating magnetic field with low frequency ( f = 192 Hz) for noninvasive magnetic nanothermometry. The achieved magnetic nanothermometer employs the measured fundamental and third harmonics in ac magnetic field (fundamental and second harmonics in ac plus dc magnetic fields), as well as the Fourier series of the first-order Langevin function, to calculate temperature. Our experimental result shows that the maximum error of temperature probing is about 0.67 K with a standard deviation of 0.29 K in ac magnetic field whereas it is about 0.48 K with a standard deviation of 0.19 K in ac plus dc magnetic fields with response time of 1 s. Furthermore, experimental results indicate that an increase in response time from 1 to 8 s improves the accuracy of temperature probing from 0.29 to 0.08 K in ac magnetic field (from 0.19 to 0.06 K in ac plus dc magnetic fields). In addition, the dependence of temperature probing accuracy on measurement signal-to-noise ratio of magnetic nanoparticle magnetization spectrum is discussed by comparing the measured second and third harmonics, which are induced in ac + dc and ac magnetic fields, respectively. [ABSTRACT FROM AUTHOR]

Tailoring the properties of superparamagnetic nanoparticles (MNPs) is essential for various nano-based biological applications. Having control over the properties of the MNPs permits a maximum flexibility. Starting from monodisperse iron oxide MNPs produced by thermal decomposition, we report on the optimization and characterization of a first and second seed mediated growth step by varying the surfactant amount and by optimizing the heating steps. We demonstrate the ability to gradually increase the size of crystalline MNPs from 6 over 9 to 12 nm with an improving monodispersity as demonstrated by Transmission Electron Microscopy, Dynamic Light Scattering and X-ray diffraction. The magnetic properties of the MNPs, studied by Vibrating Sample Magnetometry, were in concert with their size increase. We also show the functionalization of these particles with polyethylene glycolated silanes, to render the MNPs stable in water. Different characterization techniques, namely Transmission Electron Microscopy, Dynamic Light Scattering, Fourier-transform InfraRed, Thermo gravimetric analysis and X-ray Photoelectron Spectroscopy, confirmed the successful engraftment of the silanes on the MNP's surface. In conclusion, the proposed route of step-wise synthesis in combination with silane functionalization allows fine tuning the physical properties of iron oxide MNPs for applications in an aqueous environment. [ABSTRACT FROM AUTHOR]

A detection scheme for both Brownian and Néel relaxation of magnetic nanoparticles (MNPs) is demonstrated by a mixing-frequency method in this paper. MNPs are driven into the saturation region by a low-frequency sinusoidal magnetic field. A high-frequency sinusoidal magnetic field is then applied to generate mixing-frequency signals that are highly specific to the Brownian relaxation of MNPs. These highly sensitive mixing-frequency signals from MNPs are picked up by a pair of balanced built-in detection coils. The relationship between MNPs' relaxation time and phase delays of the mixing-frequency signals behind the applied field is derived, and is experimentally verified. Magnetite MNPs with the core diameter of 35 nm are used for the measurement of Brownian relaxation, and Magnetite MNPs with the core diameter of 12 nm are used for the measurement of Néel relaxation. The results show that both Brownian and Néel relaxation depend on the magnetic offset field. This study provides an in-depth understanding of the relaxation mechanisms of MNPs. [ABSTRACT FROM AUTHOR]

The preservation of the bioreactivity of antibodies and proteins by immobilization on the surface of magnetic nanoparticles is essential for particle targeting applications in diagnosis and therapy. Here we compare the conjugation of a model antibody and of streptavidin to the surface of biocompatible 100 nm magnetic starch nanoparticles by strain-promoted alkyne-azide cycloaddition (SPAAC) with the established carbodiimide and maleimide chemistry. Under our reaction conditions the bioreactivity of the immobilized antibody was about 28% for the random amide bond formation using carbodiimide chemistry, the bioreactivity increased to about 61% for bioorthogonal SPAAC and to about 90% for maleimide conjugation. The same order was found for the biotin binding capacity of streptavidin, that was conjugated to the magnetic nanoparticles with the same methods. The described analytical methods are a platform for further studies with improved bioorthogonal conjugation reactions, e.g. the strain-promoted alkyne-nitrone cycloaddition (SPANC). [ABSTRACT FROM AUTHOR]

A detection scheme for hydrodynamic size distribution of magnetic nanoparticles (MNPs) is demonstrated by a mixing-frequency method in this paper. MNPs are driven into the saturation region by a low frequency sinusoidal magnetic field. A multi-tone high frequency sinusoidal magnetic field is then applied to generate mixing-frequency signals that are highly specific to the Brownian relaxation of MNPs. These highly sensitive mixing-frequency signals from MNPs are picked up by a pair of balanced built-in detection coils. The relation between MNPs' hydrodynamic size distribution and phase delays of the mixing-frequency signals behind the applied field are derived, and are experimentally verified. Iron oxide MNPs with the core diameter of 30 nm are used for the measurement of Brownian relaxation. The results are fitted well with Debye model. This study provides a volume-based magnetic sensing scheme for the real-time measurement of MNPs hydrodynamic size distribution. [ABSTRACT FROM PUBLISHER]

Magnetic nanoparticles functionalized with carboxyl-group have considerable potential to be used as bio-labels due to their conjugation abilities with proteins. Here, we synthesized the iron oxide nanoparticles functionalized with carboxyl groups through self-assembled monolayer coating using citric acid and self-assembled bilayer coating using fatty acids. Their dimension, hydrodynamic size, surface property, and magnetic behavior were characterized through transmission electron microscopy, dynamic light scattering, Fourier transform infrared spectroscopy, thermal gravimetric analysis, and vibrating sample magnetometry. We also confirmed the binding ability of these nanoparticles with bovine serum albumin on thin gold film. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles can be employed for a broad range of biomedical applications where the knowledge of the distribution of the magnetic nanoparticles is of importance for efficacy, patient's safety, etc. The need exists to have an as accurate as possible quantification of the unknown particles distribution. Magnetorelaxometry (MRX) measurements are able to measure the magnetic induction originating from a certain distribution of magnetically activated nanoparticles. Starting from these measurements it is possible to determine the distribution using a minimum norm estimation technique. This approach is however ill-posed. We sequentially activate the magnetic nanoparticles through the use of excitation coil arrays with the aim to reduce the ill-posedness. This paper presents some advancements in magnetic nanoparticle reconstruction in terms of reconstruction quality using numerical simulations. The results show that inhomogeneous sequential activation is a proper alternative to homogeneous activation with Helmholtz coils since an increase in accuracy with a factor ranging from 1.5 until 2 is obtained. The presented numerical techniques coupled to MRX measurements can be of significant aid so to have more quantitative knowledge of the biodistribution. [ABSTRACT FROM PUBLISHER]

We present a review of giant magnetoresistance (GMR) spin valve sensors designed for detection of magnetic nanoparticles as biomolecular labels (nanotags) in magneto-nano biodetection technology. We discuss the intricacy of magneto-nano biosensor design and show that as few as approximately 14 monodisperse 16-nm superparamagnetic Fe3 O4 nanoparticles can be detected by submicron spin valve sensors at room temperature without resorting to lock-in (narrow band) detection. GMR biosensors and biochips have been successfully applied to the detection of biological events in the form of both protein and DNA assays with great speed, sensitivity, selectivity, and economy. The limit of molecular detection is well below 10 pM in concentration, and the protein or DNA assay time can be under two hours. The technology is highly scalable to deep multiplex detection of biomarkers in a complex disease, and amenable to integration of microfluidics and CMOS electronics for portable applications. On-chip CMOS circuitry makes a sensor density of 0.1-1 million sensors per square centimeter feasible and affordable. The theoretical and experimental results thus far suggest that magneto-nano biochip-based GMR sensor arrays and nanotags hold great promise in biomedicine, particularly for point-of-care molecular diagnostics of cancer, infectious diseases, radiation injury, cardiac diseases, and other diseases. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles with a core/shell structure were fabricated by a sol-gel method and following hydrogen reduction process. The reduction process changed the crystal structure of synthesized nanoparticles from iron-oxide single phase to iron phase covered with an iron-aluminum oxide shell layer. These nanoparticles were dispersed by homogenizing and ultrasonication in order to form ferromagnetic ink. Using synthesized ink, patterns with soft magnetic properties were successfully printed on Si substrates by a direct printing method. [ABSTRACT FROM AUTHOR]

The goals of this study were first to prepare and second to test albumin-based beads containing maghemite nanoparticles disperded on them. Incorporation of maghemite nanoparticles in the albumin-based template, allowing full control of the magnetic content, was accomplished by adding ionic magnetic fluid to the albumin suspension, following heat denaturation. The material evaluation was performed using Zeta potential measurements and scanning electron microscopy from one side and by investigating the cell activity on the other hand. [ABSTRACT FROM AUTHOR]

We present an analytical model for detection of multiple magnetic nanoparticles (NP) as biomolecular labels by spin valve (SV) sensors, aiming to establish the relationship between the SV sensor signal and the number of magnetic labels. The model is based on the assumptions of equivalent average field of magnetic NPs and the coherent magnetization rotation of SVs free layer. Using the model, we have calculated the sensor signals of multiple NPs uniformly or randomly distributed over a SV sensor at various aspect ratios of the NP array. Satisfactory signal linearity at low particle number or high aspect ratio has been found. The model also reveals that the SV sensors could be made insensitive to the random configuration of NPs and only sensitive to the number of NPs. This feature is desired for quantitative bio-detection. To check the validity of the model, we performed experiments on a monolayer of 16-nm Fe3O4 NPs coated on 0.3-μm-wide SV sensors. We found that the measured signals could be well described by the analytical model. [ABSTRACT FROM AUTHOR]