H. E. Horng

Ordered structures in Fe3O4 kerosene-based ferrofluids

The patterns of kerosene-based ferrofluid films in applied parallel and perpendicular magnetic fields were studied. The time dependence of quasiperiodic chains in a parallel magnetic field, the perfect hexagonal crystal structure in a weaker perpendicular field, and the labyrinthine pattern in a stronger perpendicular field were observed. The Fe3O4 kerosene-based ferrofluids that we used in this study were synthesized by the coprecipitation method. As the parallel external magnetic field was applied to a ferrofluid film, the ordered quasiperiodic chains were obtained. On the other hand, the initial nonequilibrium disordered quantum columns were formed in an applied perpendicular magnetic field, and an equilibrium hexagonal structure with columns occupying its vortices was formed after two hours. The distance between these columns decreases as the strength of the applied magnetic field increases, and hence, the patterns change gradually from the hexagonal structure to a labyrinthine pattern with the streng...

Origin of field-dependent optical transmission of magnetic fluid films

The physical mechanism of the optical transmission of magnetic fluid films under perpendicular magnetic fields is investigated in this work. Under perpendicular magnetic fields, originally dispersed magnetic particles agglomerate to form magnetic columns. The liquid phase is transparent, whereas the columns are opaque. Hence, the liquid phase dominates the optical transmission of the magnetic fluid film. When the field strength is raised, more columns are formed, and the area of the liquid phase is reduced. This leads to the decrease in the optical transmission of the film under higher field strength. The variation in the concentration of the liquid phase under various field strengths also contributes to the transmission of the film. By taking account of the variations of the effective concentration and the area ratio of the liquid phase in the magnetic fluid film under magnetic fields, the resultant magnetic field dependence of the optical transmission was calculated and found to be consistent with the experimental results. This provides evidence for the origin of the field-dependent optical transmission of the magnetic fluid film under external fields.

Biofunctionalized magnetic nanoparticles for high-sensitivity immunomagnetic detection of human C-reactive protein

In this work, we developed immunomagnetic detection techniques for detecting human C-reactive protein (CRP). To enhance the technique’s sensitivity to human CRP, biofunctionalized magnetic nanoparticles were used as markers, and a superconductive quantum interference device gradiometer system was adapted to measure the saturated magnetization of magnetically labeled CRP–anti-CRP immune complexes. Sensitivity for human CRP was found to be as high as 1ng in 0.1ml, i.e., 10ng∕ml in concentration. This sensitivity is much higher than that of conventional enzyme linked immunosorbent assay by one order of magnitude.

Wash-free immunomagnetic detection for serum through magnetic susceptibility reduction

In this study, a platform for wash-free immunomagnetic detections is discussed. The reagent is a magnetic fluid composed of biofunctionalized magnetic particles dispersed in water. The assay instrument is a mixed-frequency magnetosusceptometer. The mixed-frequency ac magnetic susceptibility χac of the magnetic reagent is reduced, as a result of the formation of magnetic clusters via the association among magnetic nanoparticles and a specific biotarget. The immunoassay detection of proteins in water, such as aqueous c-reactive protein, is characterized and is compared to that in serum. These observations demonstrate the advantages of high convenience, high sensitivity, and high specificity for χac-reduction immunomagnetic detection.

Nanomagnetic particles for SQUID-based magnetically labeled immunoassay

With the increasing importance of SQUID-based magnetically labeled immunoassay, the study on the synthesis of controllable sizes of magnetic nanoparticles plays a role to promote the accuracy of the immunoassay. In this work, Fe/sub 3/O/sub 4/ nano-particles coated with a suitable bio-probe (biotin) are synthesized through chemical co-precipitation process to probe the bio-target (avidin). Through the synthesis developed here, the particle hydrodynamic diameter can be adjusted from 30 to 90 nm, which provide candidates for probing various bio-targets in the future. The amount of the magnetically labeled avidin is then analyzed via measuring the saturated magnetization or the remanence of the sample by using a SQUID magnetometer.

Magnetic relaxation measurement in immunoassay using high-transition-temperature superconducting quantum interference device system

Due to their ultrahigh sensitivity to magnetic flux, superconducting quantum interference devices (SQUIDs) are able to detect biomagnetic signals. By labeling biotargets with magnetic nanoparticles, several groups have shown that SQUIDs are promising as quantitative probes of biotargets by measuring their magnetic properties. In this work, we describe the design and construction of a high-transition-temperature radio-frequency SQUID magnetometer system for measuring the magnetic relaxation of labeled avidin. We also describe the synthesis of magnetic nanoparticles coated with biotin for use in labeling the avidin. Furthermore, the specifications of the SQUID-based magnetically labeled immunoassay of avidin are explored.

Electron transport and magnetic properties of the icosahedral Al - Pd - Re quasicrystals

The temperature dependence of the conductivity of Al - Pd - Re quasicrystals can be described by a power law, that is, is different in low- and high-temperature regimes for high-quality samples. At high temperatures, the conductivity is found to be closely related to the inverse Hall coefficient. The magnetic susceptibility of Al - Pd - Re quasicrystals is negative. At low temperatures the magnitude of is seen to decrease quite rapidly with increasing temperature. between 2 and 400 K can be described well by the following relation: . The possible origins of each of the terms are discussed in this paper.

Multi-Channel SQUID-Based Ultra-High-Sensitivity In-Vitro Detections for Bio-Markers of Alzheimer's Disease Via Immunomagnetic Reduction

Via immunomagnetic reduction assay, bio-molecules can be quantitatively detected with the aid of bio-functionalized magnetic nanoparticles, which are used as labeling markers for specific bio-molecules. To achieve an ultra-high sensitivity in the detection of bio-molecules, the superconducting quantum interference device (SQUID) looks very promising as a sensor for the magnetic signal that are related to the concentration of the detected bio-molecules. We had developed a single channel SQUID-based magnetosusceptometer, but for increasing the detection through-put, we have developed a multi-channel SQUID-based magnetosusceptometer. In this work, the design and the working principle of a 4-channel SQUID-based magnetosusceptometer are introduced. By utilizing scanning technology, 4 samples can be logged into a SQUID-based magnetosusceptometer simultaneously. Be noted that only one single SQUID magnetometer has been used in the magnetosusceptometer. The precision and the sensitivity of detecting bio-molecules by using a 4-channel SQUID-based magnetosusceptometer have been investigated. The detected bio-molecules are biomarkers for Alzheimers disease.

Optimum sputtering conditions on the in-situ growth of superconducting YBa2Cu3Oy films with an off-axis RF sputtering configuration

Abstract The effects of sputtering conditions on the transport properties of YBa 2 Cu 3 O y (YBCO) thin films were investigated in this work using an off-axis RF sputtering configuration. These conditions included the substrate temperature, the distance from the substrate to the target, the total pressure of the sputtering gas and the gas composition. The substrates were MgO (001) and SrTiO 3 (001) and the sputtering gas was a mixture of Ar and O 2 . The YBCO films were characterized by resistivity measurements, X-ray diffraction and scanning force microscopy (SFM). Additionally, the optimum conditions of growing high-quality YBCO films were obtained. Those conditions were found to be: (1) the substrate is 3.5 cm horizontal and 3.0 cm vertical away from center of target, (2) the substrate temperature is 680°C for MgO and it is 720°C for SrTiO 3 , and (3) the pressure of the sputtering gas of Ar : O 2 is (3 : 7) at 300 mTorr. The high-quality YBCO films revealed a transition temperature T c ( R = 0) at 87 ∼ 90 K, a normal-state resistance ratio R 300K / R 100K ∼ 3 and a normal-state resistivity at 300 K smaller than 200 μΩ cm.

Detection of deep flaws by using a HTS-SQUID in unshielded environment

We reported the nondestructive evaluation of flaws in conductive samples with the high-T/sub c/ SQUID operated at 77 K. By nulling the SQUID with an additional compensation, we can sensitively detect the excited magnetic field due to the eddy current around a deep flaw. To investigate the effects of the size and the depth of flaws on the induced magnetic field, the excited magnetic fields as a function of the depth were measured for buried slots with various widths and thickness. Besides, the amplitude and the phase with different excitation frequencies for a fixed slot size are also studied. It was found that for a fixed excitation frequency, the phase of the measured signal linearly responds to the depth of the slot, while the amplitude correlates with the height of the slot. The results are valuable for quantitative evaluation of flaws.