Concentration Of Magnetic Nanoparticles Research Articles

Effect of Magnetic Field and Nanoparticle Concentration on Melting of Cu-Ice in a Rectangular Cavity under Fluctuating Temperatures

The primary objective of the present paper is to examine the combined effect of a uniform magnetic field and nanoparticle volume fraction on the melting process of copper-water (ice) as Nano-enhanced Phase Change Material (NePCM). The NePCM is enclosed in a rectangular cavity subjected to a fluctuating temperature at the hot wall. The phase change process is formulated and solved using the Lattice Boltzmann Method. The numerical outcomes of the developed code are validated by comparing them with available experimental and numerical results in the literature. For the melting process of NePCM, the considered parameters include Hartmann number (Ha=0, 30, 60 and 90), nanoparticle volume fraction (ϕ=0, 2, 4 and 6 vol%), and Rayleigh number (Ra=103, 104 and 105). The results showed that the melting time is considerably extended at high Ra as the Ha is increased. Furthermore, addition of nanoparticles notably contributes to the shortening of melting time at low Ra, while they have an adverse effect and extends the melting time up to 7% at high Ra in the existence of magnetic field (MF). However, they decrease melting time up to 10% at Ra=105 when the MF is not applied (Ha=0). It is also noted that the influences of examined parameters become prominent for Fo>0.5. These results may help understanding the control of melting process of electrically-conducting materials, specifically the nano-enhanced energy storage materials.

Photocrosslinking and photopatterning of magneto-optical nanocomposite sol\u2013gel thin film under deep-UV irradiation

This paper is aimed at investigating the process of photocrosslinking under Deep-UV irradiation of nanocomposite thin films doped with cobalt ferrite magnetic nanoparticles (MNPs). This material is composed of a hybrid sol–gel matrix in which MNP can be introduced with high concentrations up to 20 vol%. Deep-UV (193 nm) is not only interesting for high-resolution patterning but we also show an efficient photopolymerization pathway even in the presence of high concentration of MNPs. In this study, we demonstrate that the photocrosslinking is based on the free radical polymerization of the methacrylate functions of the hybrid precursor. This process is initiated by Titanium-oxo clusters. The impact of the nanoparticles on the photopolymerization kinetic and photopatterning is investigated. We finally show that the photosensitive nanocomposite is suitable to obtain micropatterns with sub-micron resolution, with a simple and versatile process, which opens many opportunities for fabrication of miniaturized magneto-optical devices for photonic applications.

Detection method of nonlinear magnetized harmonic signal of medical magnetic nanoparticles

Medical magnetic nanoparticles are nano-medical materials with superparamagnetism, which can be collected in the tumor tissue through blood circulation, and magnetic particle imaging technology can be used to visualize the concentration of magnetic nanoparticles in the living body to achieve the purpose of tumor imaging. Based on the nonlinear magnetization characteristics of magnetic particles and the frequency characteristics of their magnetization, a differential detection method for the third harmonic of magnetic particle detection signals is proposed. It was modeled and analyzed, to study the nonlinear magnetization response characteristics of magnetic particles under alternating field, and the spectral characteristics of magnetic particle signals. At the same time, the relationship between each harmonic and the amount of medical magnetic nanoparticle samples was studied. On this basis, a signal detection experimental system was built to analyze the spectral characteristics and power spectral density of the detected signal, and to study the relationship between the signal and the excitation frequency. The signal detection experiment was carried out by the above method. The experimental results showed that under the alternating excitation field, the medical magnetic nanoparticles would generate a spike signal higher than the background sensing signal, and the magnetic particle signal existed in the odd harmonics of the detected signal spectrum. And the spectral energy was concentrated at the third harmonic, that is, the third harmonic magnetic particle signal detection that meets the medical detection requirement could be realized. In addition, the relationship between each harmonic and the particle sample volume had a positive growth relationship, and the detected medical magnetic nanoparticle sample volume could be determined according to the relationship. At the same time, the selection of the excitation frequency was limited by the sensitivity of the system, and the detection peak of the third harmonic of the detection signal was reached at the excitation frequency of 1 kHz. It provides theoretical and technical support for the detection of medical magnetic nanoparticle imaging signals in magnetic particle imaging research.

Enhanced Detection of Magnetic Nanoparticles Using a Novel Microwave Ferromagnetic Resonance Imaging System

For this proof of concept, the chamber has been equipped with four wire monopole antennas, and low-contrast oil-based targets have been tested with varying concentrations of iron oxide magnetic nanoparticles (MNP) to serve as ferromagnetic contrast agents. The electromagnet is capable of sustaining a static polarizing magnetic field (PMF) greater than 0.2Tesla (2000Gauss) across the imaging chamber to modulate the MNPs' ferromagnetic response, effectively changing the targets' magnetic permeability. Differential scattered field data are then collected through the application and withdrawal of this PMF. This study has successfully characterized a particular narrow band of frequencies within the asymmetric faceted chamber that demonstrate significant differential responses corresponding to the weak magnetic signal physically isolated from the MNPs, tested on different sizes and positions of targets containing various concentrations of MNPs. Similar to ferromagnetic resonance (FMR) spectroscopy, in which detection of FMR phenomena is best achieved at probing frequencies coinciding with the structural resonant frequency of a metallic cavity, these resonant frequencies of interest yield a high level of sensitivity to MNP permeability changes and are suitable for imaging within the chamber. These represent the first experimental results of a full-scale FRI system capable of detecting and eventually imaging MNPs at biologically relevant concentrations.

Synthesis of a thermoresponsive crosslinked MEO2MA polymer coating on microclusters of iron oxide nanoparticles

Encapsulation of magnetic nanoparticles (MNPs) of iron (II, III) oxide (Fe3O4) with a thermopolymeric shell of a crosslinked poly(2-(2-methoxyethoxy)ethyl methacrylate) P(MEO2MA) is successfully developed. Magnetic aggregates of large size, around 150–200 nm are obtained during the functionalization of the iron oxide NPs with vinyl groups by using 3-butenoic acid in the presence of a water soluble azo-initiator and a surfactant, at 70 °C. These polymerizable groups provide a covalent attachment of the P(MEO2MA) shell on the surface of the MNPs while a crosslinked network is achieved by including tetraethylene glycol dimethacrylate in the precipitation polymerization synthesis. Temperature control is used to modulate the swelling-to-collapse transition volume until a maximum of around 21:1 ratio between the expanded: shrunk states (from 364 to 144 nm in diameter) between 9 and 49 °C. The hybrid Fe3O4@P(MEO2MA) microgel exhibits a lower critical solution temperature of 21.9 °C below the corresponding value for P(MEO2MA) (bulk, 26 °C). The MEO2MA coating performance in the hybrid microgel is characterized by dynamic light scattering and transmission electron microscopy. The content of preformed MNPs [up to 30.2 (wt%) vs. microgel] was established by thermogravimetric analysis while magnetic properties by vibrating sample magnetometry.

Highly-sensitive magnetic sensor for detecting magnetic nanoparticles based on magnetic tunnel junctions at a low static field

Magnetic sensors to detect magnetic nanoparticles (MNPs) towards biomedical applications require very high sensitivity at low magnetic fields. Here we report a magnetic sensor consisting of a magnetic tunnel junction (MTJ) with a synthetic antiferromagnetic free layer. This sensor exhibits a low magnetic anisotropy and sensitivities of over 18%/Oe at low fields in the range of 0 to 3 Oe. We employ superparamagnetic MNPs with a large diameter of 200 nm. The sensor’s transfer curves show the magnetoresistance (MR) variations as a function of MNP concentration. We demonstrate the detection capability of MNP amounts of below 500 ng and low MNP concentrations of 0.01, 0.1, and 1 mg/ml in solvents. This result suggests that the combination of high-sensitivity TMR sensors and large MNPs has a substantial potential for biomarker detection applications.

Clustering in Ferronematics - The Effect of Magnetic Collective Ordering

Clustering of magnetic nanoparticles can dramatically change their collective magnetic properties and it consequently may influence their performance in biomedical and technological applications. Due to tailored surface modification of magnetic particles such composites represent stable systems. Here, we report ferronematic mixtures that contain anisotropic clusters of mesogen-hybridized cobalt ferrite nanoparticles dispersed in liquid crystal host studied by different experimental methods - magnetisation measurements, small angle X-ray scattering (SAXS), small angle neutron scattering (SANS) and capacitance measurements. The obtained results showed non-monotonic dependencies of magnetisation curves as well as of the Freedericksz transition on the magnetic nanoparticles concentration. This can be explained by the formation of clusters, whose structure was determined by SAXS measurements. Complementary to the magnetisation measurements, SANS measurements of the samples were performed for different magnetic field strength to obtain information on the orientation of the liquid crystal molecules.

Effect of Fe-=SUB=-3-=/SUB=-O-=SUB=-4-=/SUB=- nanoparticle concentration on the luminescence of AgInS-=SUB=-2-=/SUB=-/ZnS in hybrid complex CaCO-=SUB=-3-=/SUB=--Fe-=SUB=-3-=/SUB=-O-=SUB=-4-=/SUB=-@AgInS-=SUB=-2-=/SUB=-/ZnS-=SUP=-*-=/SUP=-

In this paper, we studied the properties of a multifunctional system, in which the luminescent and magnetic properties are combined. The calcium carbonate microspheres are used as porous matrices for complexes combining luminescence properties of AgInS2/ZnS quantum dots and magnetic properties of Fe3O4 nanoparticles. The study investigates the effect of magnetic nanoparticles concentration on optical properties of quantum dots in CaCO3-Fe3O4@AgInS2/ZnS complexes. It is shown that applying calcium carbonate microspheres as a matrix permits to reduce quenching of the quantum dots luminescence. Keywords: hybrid system; ternary quantum dots; magnetic nanoparticles; iron oxide; calcium carbonate microspheres.

Recovery of sperms bearing X chromosomes with different concentrations of magnetic nanoparticles in ram.

Pre-conceptual sex selection is still a highly debatable process whereby X and Y chromosome bearing spermatozoa are isolated before oocyte fertilization. Recently, magnetic nanoparticles (MNP) have been used to determine X and Y chromosomes bearing spermatozoa as a result of searching for a cheap, highly efficient method using non-toxic materials. This study aimed to recover the sperm bearing X chromosomes in ram with different concentrations of MNP and then evaluate the success of this method using polymerase chain reaction (PCR). Ram sperms were divided into four groups, treated with 0 (control), 50, 100 and 200μg/ml MNP, respectively. MNP was used to restore sperm cells bearing X chromosomes. Upon recovery, the PCR was performed to identify the X and Y sperms, Methyl ThiazoleTetrazolium (MTT), to assess MNP toxicity and sperm viability and acridine orange (AO) to evaluate sperm DNA integrity. The results of PCR revealed that the treatment of spermatozoa- bearing X chromosomes with 50μg/ml MNP had the highest effects on the recovery of X sperm rather than the other concentrations of MNP. However, the concentrations of MNP didnothaveany toxic effects on spermatozoa, sperm viability and, DNA integrity, but the high concentration of MNP (200μg/ml) significantly reduced DNA integrity. According to MTT and AO results, the concentrations of MNP used in this study had no toxic effects on spermatozoa and did not reduce the sperm viability and DNA integrity, except that 200μg/ml MNP significantly reduced DNA integrity.

Simulation research on the forward problem of magnetoacoustic concentration tomography for magnetic nanoparticles with magnetic induction in a saturation magnetization state

Magnetoacoustic concentration tomography of magnetic nanoparticles (MNPs) with magnetic induction (MACT-MI) is a method that has been propsed recently for MNP concentration tomography for use in targeted therapy. This procedure has the advantages of being noninvasive, having high-resolution and providing quantitative estimation of MNPs. In order to further fundamentally increase the signal-to-noise ratio of the magnetoacoustic signal, the forward problem of MACT-MI in the saturation magnetization state was studied, especially the magnetization characteristics of MNPs, including the derivation of the force formula of MNPs in the saturation magnetization state and the relationships among the gradient of the external magnetic field, magnetic force, number concentration and sound pressure. Firstly, the magnetic force formula of MNPs in the saturation magnetization state was derived according to the classical Langevin theory of paramagnetism. Then, a 2D model was constructed to calculate the magnetic flux density, magnetic force and sound pressure. Finally, the 2D distribution diagram of magnetic force and sound pressure and its corresponding 1D curve were obtained. The simulation results showed that the saturation magnetic field produced by the Maxwell–Helmholtz coils made the MNPs magnetically saturated. Compared with the MNPs in an unsaturated magnetization state, the magnetic force of MNPs in the saturation magnetization state was stronger, and the stronger magnetic force could generate stronger magnetoacoustic signals, which made it possible to measure magnetoacoustic signals with higher signal-to-noise ratio. The research results can provide a research basis for the design of equipment for further MACT-MI experiment and clinical application.

A Magnetic Particle Imaging-Based Navigation Platform for Magnetic Nanoparticles Using Interactive Manipulation of a Virtual Field Free Point to Ensure Targeted Drug Delivery

Magnetic nanoparticles (MNPs) exhibiting certain superparamagnetic properties are optimal for drug delivery because they facilitate imaging and targeting of biological interactions at the cellular and molecular levels. In terms of monitoring, magnetic particle imaging (MPI) yields real-time MNPs position and concentration data, and guides MNPs to desired positions if an actuation function is available. Here, we describe a new, user-driven steering scheme for MNPs based on a virtual field free point (FFP). The scheme utilizes a general MPI system, with no need for additional hardware. The scheme facilitates interactive user manipulation with real-time imaging and MNPs actuation within the body. An FFP with four coils is used to model the resultant magnetic force and a virtual FFP to linearize that force with respect to the relative positions of the MNPs and the real FFP. Simulations and experiments confirm that the direction and magnitude of the forces exerted on MNPs via manipulation of the virtual FFP are controllable. An intuitive guidance system featuring real-time MPI at 2 Hz and user-driven virtual FFP manipulation (via a computer mouse) is employed to show that MNPs trajectories can be controlled. Our MPI-based navigation platform allows the user to effectively guide MNPs using real-time visual feedback, facilitating targeted drug delivery.

Discontinuous Dewetting in a Degassed Mold for Fabrication of Homogeneous Polymeric Microparticles.

Discontinuous dewetting (DD) is an attractive technique that enables the production of large liquid arrays in microwells and is applicable to the synthesis of anisotropic microparticles with complex morphologies. However, such loading of liquids into microwells presents a significant challenge, as the liquids used in this technique should exhibit low mold surface wettability. This study introduces DD in a degassed mold (DM), a simple yet powerful technique that achieves uniform loading of microparticle precursors into large microwell arrays within 1 min. Using this technique, hydrogel microparticles are produced by different polymerization mechanisms with various shapes and sizes, ranging from a few micrometers to hundreds of micrometers. Hydrophobic oil microparticles are produced by the simple plasma treatment of the DM, and agarose microparticles encapsulating bovine serum albumin (in a well-dispersed state) are produced by submerging the DM in fluorinated oil. To demonstrate additional functionality of microparticles using this technique, high concentrations of magnetic nanoparticles are loaded into microparticles for particle-based immunoassays performed in a microwell plate, and the immunoassay performance is comparable to that of ELISA.

Study of Structural Changes in Nematic Liquid Crystals Doped with Magnetic Nanoparticles Using Surface Acoustic Waves

The surface acoustic waves (SAWs) were used to study the effect of magnetic nanoparticles on nematic liquid crystal (NLC) behavior in weak magnetic and electric fields. The measurement of the attenuation of SAW propagating along the interface between piezoelectric substrate and liquid crystal is showed as an effective tool to study processes of structural changes. The magnetic nanoparticles Fe3O4 of nanorod shape and different low volume concentration were added to the NLC (4-(trans-4′-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT)) during its isotropic phase. In contrast to undoped liquid crystals the distinctive different SAW attenuation responses induced by both magnetic and also electric fields in studied NLC samples were observed suggesting both structural changes and the orientational coupling between both magnetic and electric moments of nanoparticles and the director of the NLC molecules. Experimental measurements including the investigation under linearly increasing and/or jumped magnetic and electrical fields, respectively, as well as the investigation of temperature and time influences on structural changes were done. The investigation of the SAW anisotropy gives supplemental information about the internal structure of nanoparticles in investigated NLCs. In addition, some magneto-optical investigations were performed to support SAW results and study their stability and switching time. The analysis of observed SAW attenuation characteristics confirmed the role of concentration of magnetic nanoparticles on the resultant behavior of investigated NLC compounds. Obtained results are discussed within the context of previous ones. The theoretical background of the presented SAW investigation is introduced, too.

On the measurements of magnetic nanoparticle concentration in a biological medium using a superconducting quantum magnetometer

Magnetic nano-particles are used in medicine both as medical means, and for the transport of medicines in the pathological area of an organism. Simultaneous influence on these particles of ultrasonic radiation and a constant magnetic field allows summarising a magnetic field of an nano-particles ensemble to the value, sufficient for its registration by the remote magnetic detector. The parity connecting the measured magnetic flux of the nanoparticles with parameters of the particles, ultrasound, and the measuring system using as the magnetic detector superconducting quantum magnetometer is received. Calculations have shown, that such a system can measure a concentration of the nano-particles in colloidal solution, modeling the biological medium, in the unattainable earlier dynamic range of values (from 1 vol % to 10−7 vol %).

A comparative investigation of normal and inverted exchange bias effect for magnetic fluid hyperthermia applications

Exchange bias (EB) of magnetic nanoparticles (MNPs) in the nanoscale regime has been extensively studied by researchers, which have opened up a novel approach in tuning the magnetic anisotropy properties of magnetic nanoparticles (MNPs) in prospective application of biomedical research such as magnetic hyperthermia. In this work, we report a comparative study on the effect of magnetic EB of normal and inverted core@shell (CS) nanostructures and its influence on the heating efficiency by synthesizing Antiferromagnetic (AFM) NiO (N) and Ferrimagnetic (FiM) Fe3O4 (F). The formation of CS structures for both systems is clearly authenticated by XRD and HRTEM analyses. The magnetic properties were extensively studied by Vibrating Sample Magnetometer (VSM). We reported that the inverted CS NiO@Fe3O4 (NF) MNPs have shown a greater EB owing to higher uncompensated spins at the interface of the AFM, in comparison to the normal CS Fe3O4@NiO (FN) MNPs. Both the CS systems have shown higher SAR values in comparison to the single-phased F owing to the EB coupling at the interface. However, the higher surface anisotropy of F shell with more EB field for NF enhanced the SAR value as compared to FN system. The EB coupling is hindered at higher concentrations of NF MNPs because of the enhanced dipolar interactions (agglomeration of nanoparticles). Both the CS systems reach to the hyperthermia temperature within 10 min. The cyto-compatibility analysis resulted in the excellent cell viability (> 75%) for 3 days in the presence of the synthesized NPs upto 1 mg/ml. These observations endorsed the suitability of CS nanoassemblies for magnetic fluid hyperthermia applications.

Evaluation of the interaction of a guanylhydrazone derivative with cobalt ferrite nanoparticles and PAMAM electrochemical and UV/visible spectroscopic techniques

Nowadays, scientific research grows a lot around nanotechnology, which connects many areas of knowledge such as electrochemistry and magnetic nanoparticles (MNPs). The study of bioactive substances by electrochemical methods is already very conceptual, and the association of magnetic nanoparticles has emerged as a new bias of this technique. Here, we report the results of the interaction between the molecule LQM10, a derivative of guanylhydrazone, with nanocarriers: cobalt ferrite magnetic nanoparticles (CoFe2O4 MNPs) and polyamidoamine dendrimer (PAMAM), seeking to unite the characteristics of each nanocarrier to benefit LQM10. The electrochemical system was composed of 3 electrodes, Ag/AgCl/Cl− saturated (reference), platinum (auxiliary), and modified glassy carbon (GCE) (work) with CoFe2O4 MNPs alone and with PAMAM G3, in buffered medium pH 7.03 with or without a co-solvent (analytical grade ethanol). UV-visible spectroscopic studies were carried out in aqueous-ethanolic medium in different concentrations of PAMAM G3 and CoFe2O4 MNPs. The magnetic properties of CoFe2O4 MNPs and each nanocarriers were confirmed by vibrating sample magnetometer and by field effect calorimetry. LQM10, which has a redox profile in oxidative potentials, showed good interaction with all tested electrodes and revealed considerable values of formation constant (KF), highlighting the GCE modified with CoFe2O4 MNPs (KF = 1.92 × 106 L/mol) and PAMAM G3, corroborating with the results of UV-visible data (Kb = 7.60 × 105 L/mol). The generation of heat by magnetic hyperthermia of CoFe2O4 MNPs in the presence of PAMAM G3 and LQM10 was determined (SAR = 0.72 W/g). Therefore, we demonstrated the association of promising nanocarriers (PAMAM G3 and CoFe2O4 MNPs) with anticancer substances and their applicability as magnetic hyperthermia.

Numerical simulation of the effect of necrosis area in systemic delivery of magnetic nanoparticles in hyperthermia cancer treatment.

In a magnetic hyperthermia treatment, malignant cancerous cells are ablated by the heat production of magnetic nanoparticles (MNP) under an external magnetic field. This novel approach is a promising tool to eliminate the tumor cells by a higher temperature inside the tumor microenvironment. MNPs are needed inside the tumor microenvironment to increase the heat, and this could be possible with intravenous drug injection. However, tumors with necrosis regions are more resistant to drug penetration, and this can cause inadequate and non-homogeneous temperature distribution in the tumor. Hence, in this study, we used numerical methods to investigate the Spatio-temporal temperature field distribution in the necrotic tumor and its surrounding tissue. To this end, an intravenous bolus injection is used to simulate the effect of systemic drug delivery in tumors with necrosis region. Results show that the temperature field with the necrosis region with 10% of the tumor radius is more prone to higher temperature values. The hypoxia region is affected by the high temperature despite the necrosis region in the tumor. However, a broader necrosis region impedes drug penetration inside the inner layers of tumors, which leads to a lower heat generation by the MNPs. Results also demonstrate that only 15.5% of MNP concentration distributed to the necrosis with 50% of tumor radius, leading a temperature of 42∘C in the necrosis region, which is not sufficient for the tumor ablation. Therefore, the temperature distribution is dependant on the sizes of necrosis regions in tumors, and tumors with a larger necrotic region (over 20% of tumor radius) are challenging to treat with hyperthermia treatment. This study could help the future in vitro and in vivo studies of hyperthermia treatment in necrotic tumors.

Imaging of Magnetic Nanoparticles Using Small TMR Sensor With an Excitation-Compensation Scheme

Magnetic nanoparticle imaging (MPI) is an emerging non-invasive technique with potential applications in bio-medical diagnostic and material science. In this paper, we propose a new method for MPI using tunnel magnetoresistance (TMR) sensor with an area of dimensions 0.45 mm*0.45 mm. The small size of the sensor promotes high level of integration and fine spatial resolution for magnetic field measurements. A solenoid excitation coil carrying alternating current is used to magnetize the magnetic nanoparticles (MNPs). We used commercial MNPs solution named synomag ®-D with iron concentration 10 mg/ml as sample. The response of the MNPs is measured by the TMR sensor during a 2D raster scan resulting in a magnetic image. In order to eliminate the negative effect of the strong background field from the excitation coil, a compensation coil which is located close to the TMR sensor is utilized to subtract the background signal in situ during measurements. Comparing the experimental results with and without the compensation scheme shows that the setup with the compensation coil cancels 95% of the background signal and increases the signal to noise ratio (SNR) from 7 dB to 10 dB. Mainly considering the tradeoff of 1/${f}$ noise and the MNPs response to the excitation frequency, the operating frequencies of 135 Hz, 235 Hz and 335 Hz were investigated in this study. Experimental results show that the system is capable of imaging $5~\mu \text{L}$ MNPs solution with a 5 mm lift-off from the sensor to the top surface of the MNPs sample. Furthermore, an `L' shape formed by 6 holes with $1~\mu \text{L}$ MNPs solution in each is imaged by the system. In comparison, it is very challenging for conventional MPI with coils as pickup sensors to image $10~\mu \text{g}$ irons in $1~\mu \text{L}$ MNPs solution at the low operating frequency. This is because TMR sensor has much better sensitivity than coils in the low frequency range. This work demonstrates the feasibility of using small TMR sensor with an excitation-compensation scheme for MPI. The advantages of high sensitivity, fine spatial resolution and low cost of the probe make it a promising alternative for future bio-medical research to measure the 3-D location and concentration of magnetic nanoparticles.

Dependence of biomolecule detection on magnetic nanoparticle concentration

This paper investigates the influence of magnetic nanoparticle (MNP) concentration on biomolecule detection with magnetic particle spectroscopy (MPS). Streptavidin-coated MNPs, dominated by Brownian relaxation, are used to detect biotinylated Immunoglobulin G (IgG). The conjugation of the biotinylated IgG onto the surface of the functionalized MNPs enlarges their hydrodynamic sizes, thus increasing the Brownian relaxation time and changing the MPS signal. Experimental samples are prepared with Brownian relaxation-dominated MNP samples with different mole concentrations from 6.67 to 0.67 nM and IgG samples with different mole concentrations from 0 to 8.33 nM. Experimental results of ac susceptibility spectra indicate that the Brownian relaxation time increases from 0.85 to 1.20 ms with decreasing the MNP concentration from 6.67 to 0.67 nM at a given IgG concentration of 5 nM. Experimental results of MPS show that the ratio of the 3rd to 1st harmonics decreases more significantly with increasing IgG concentration at a lower MNP concentration. The absolute variation in the ratio of 3rd to 1st harmonics of the MNPs is used to characterize the measurement sensitivity of IgG. It shows that the measurement sensitivity increases from 1.68 × 10−3 to 12.25 × 10−3 nM−1 at an excitation frequency of 180 Hz. This study demonstrates that a lower MNP concentration can improve the measurement sensitivity of biomolecules with MPS in the frequency range from 180 to 1418 Hz. We emphasize that our findings are of great importance to reach a highly sensitive approach for biomolecule detection.

Investigation of magnetically driven passage of magnetic nanoparticles through eye tissues for magnetic drug targeting

This paper elucidates the feasibility of magnetic drug targeting to the eye by using magnetic nanoparticles (MNPs) to which pharmaceutical drugs can be linked. Numerical simulations revealed that a magnetic field gradient of 20 T m−1 seems to be promising for dragging magnetic multicore nanoparticles of about 50 nm into the eye. Thus, a targeting magnet system made of superconducting magnets with a magnetic field gradient at the eye of about 20 T m−1 was simulated. For the proof-of-concept tissue experiments presented here the required magnetic field gradient of 20 T m−1 was realized by a permanent magnet array. MNPs with an optimized multicore structure were selected for this application by evaluating their stability against agglomeration of MNPs with different coatings in water for injections, physiological sodium chloride solution and biological media such as artificial tear fluid. From these investigations, starch turned out to be the most promising coating material because of its stability in saline fluids due to its steric stabilization mechanism. To evaluate the passage of MNPs through the sclera and cornea of the eye tissues of domestic pigs (Sus scrofa domesticus), a three-dimensionally printed setup consisting of two chambers (reservoir and target chamber) separated by the eye tissue was developed. With the permanent magnet array emulating the magnetic field gradient of the superconducting setup, experiments on magnetically driven transport of the MNPs from the reservoir chamber into the target chamber via the tissue were performed. The resulting concentration of MNPs in the target chamber was determined by means of quantitative magnetic particle spectroscopy. It was found that none of the tested particles passed the cornea, but starch-coated particles could pass the sclera at a rate of about 5 ng mm−2 within 24 h. These results open the door for future magnetic drug targeting to the eye.