Jiann-Yeu Chen

Magneto-Optical Kerr Effect Enhanced by Surface Plasmon Resonance and Its Application on Biological Detection

We investigated the magneto-optical Kerr signals enhanced by surface plasmon resonance (SPR) and its application of the biomolecular detection. We measure the SPR curve obtained in multilayered metallic structures (t nm Co/45 nm Au) with varying cobalt thickness t. The thicker cobalt layer causes the weaker SPR. The magneto-optical signals also receive different magnitude of amplification due to measuring the hysteresis loop on different segments of the SPR curve via magneto-optical Kerr effect (MOKE). It also worth noticing that the magneto-optical signals from the reflectance maximum or reflectance minimum of SPR would be enhanced significantly, if the thickness of Co is within the range of 3 to 28 nm. By measuring and analyzing the magneto-optical signals from samples with different thicknesses of Co, we determined an optimal thickness of 8 nm where the signal amplification is the largest. In biomedical applications, this combined system is able to lead as a sensitive biomolecule sensing. We have verified the feasibility via fetal bovine serum (FBS) attached.

Comparing the magnetic property of shell thickness controlled of Ag-Ni core-shell nanoparticles

In this paper, we studied the critical diameter of superparamagnetic core-shell particles. One pot method and microwave-assisted technique were used to synthesize Ag-Ni core-shell nanoparticles with diameters of 10 nm and 30 nm. From the experimental results of hysteresis (M-H curves) and temperature dependent magnetization (M-T curves), the theoretical critical diameter does not agree with the experimental observation of the core-shell structure. Furthermore, the blocking temperature equation should be reconsidered.

Study of polyvinyl alcohol nanofibrous membrane by electrospinning as a magnetic nanoparticle delivery approach

Electrospinning technique was used to fabricate polyvinyl alcohol (PVA)-based magnetic biodegradable nanofibers. PVA solution was mixed with ferrofluid or magnetic nanoparticles (MNPs) powder and formed two individual nanofibrous membranes (PVA/ferrofluid and PVA/MNPs powder) by electrospinning. The surface morphology of the nanofibrous membrane was characterized by scanning electron microscopy and the magnetic properties were measured by vibrating sample magnetometer. Macrophages (RAW 264.7) were co-cultured with the nanofibrous membranes for 12, 24, and 48 h and exhibited good cell viability (>95%). Results showed that the PVA fibers would be degraded and the embedded Fe3O4 nanoparticles would be released and delivered to cells.

Optimization of Magnetic Labeling Process for Intracellular Hyperthermia in Cervical Cancer Cells

Effective therapies for malignant tumors are needed, and magnetic hyperthermia has shown positive results in biomedical studies. Here, we optimize the magnetic labeling process for intracellular hyperthermia and evaluate the cytotoxicity effects of cervical cancer cell (HeLa) mediated by intracellular hyperthermia. Experimentally, cells were incubated with different concentrations of 10 nm anionic iron oxide nanoparticles, and the incubation times varied from 6 to 24 h. Iron stain (Prussian blue) and magnetophoresis were performed to evaluate the efficiency of cells internalizing the nanoparticles. An optimized condition for intracellular magnetic label was obtained, and a trypan blue exclusion test analyzed the cytotoxicity effects after cells were exposed to ac magnetic field ( f = 21 kHz, H = 4 kA/m). Cell viabilities decreased to 49% ~ 50% immediately after 120 s of treatment. After culturing the cells for 48 h, it was found that only 5% ~ 8% of cells remained viable.

Surface plasmon induced enhancement with magneto-optical layer

In this study, we examined surface plasmon resonance (SPR) induced magneto-optical (MO) Kerr signals, and obtained a complete SPR curve in multilayered metallic structures comprising 6-nm-thick Au, t-nm-thick Permalloy (Py), and 26-nm-thick Au layers (with various thicknesses of Py). As the thickness of the Py layer increased, the SPR weakened. The MO signals were exhibited to various magnitudes of amplification while measuring the hysteresis loop at different segments of the SPR curve, which were the product of the MO Kerr effect. The MO signals between the reflectance maximum and reflectance minimum of the SPR were enhanced significantly in the samples with a 2 to 20-nm-thick Py layer. After measuring and analyzing the MO signals from multiple specimens with various thicknesses of Py, the optimal thickness of the Py layer was 10 nm, at which the strongest signal amplification was obtained.

Honeycomb-shaped magnetic multilayer thin films for cell trapping

Honeycomb-shaped magnetic thin films with domain wall (DW) pinning geometry are designed to actively trap magnetically labeled cells. After an initial in-plane magnetic field (Hinitial) is applied and later reduced to zero, the resultant magnetization became locally aligned. Human hepatocellular liver carcinoma cell line (HepG2) stably expresses green fluorescent protein (GFP) and is magnetically labeled with superparamagnetic magnetic nanoparticles (MNPs). Prussian blue stain and single cell magnetophoresis are performed to evaluate the internalization of the MNPs. Magnetically labeled cells are then trapped by the stray fields of head-to-head DWs (HH DWs) or tail-to-tail DWs (TT DWs). After co-culturing with magnetic structure, HepG2 cells stretched out and showed filopodia-like protrusions to make contact with adjacent cells.

Magnetic cantilever actuator with sharpened magnetic thin film ellipses

A SiO2 cantilever covered by elliptical magnetic thin films was designed as an actuator. Under magnetic field, the elliptical magnetic film with sharp ends would exhibit single-domain structures and generate torque to push or pull the two arms of the cantilever. The cantilever could then stretch or compress and the displacement could be controlled by adjusting the magnitude and direction of the external magnetic field. The combination between micromagnetism of patterned films and actuator was successfully demonstrated. The magnetic actuator can be applied for future application in the biological field and would be valuable for microelectromechanical systems (MEMS).

Alternating magnetic field assisted magnetization reversal in ferromagnetic antidot

Although the effects of high-frequency electromagnetic waves on magnetization reversal have been extensively studied, the influence of a low-frequency ac field on magnetization reversal has seldom been examined. In this study, we measured the magnetoresistance and examined the magnetic switching process of Permalloy antidot thin films under an alternating magnetic field with a frequency of 25 kHz. When no alternating magnetic field was present, the transitional field of the antidot thin films decreased as the angle of the direct magnetic field increased. When an alternating magnetic field was present, the transitional field exhibited the same trend. We compared the magnetization process of the antidot thin films with and without the alternating magnetic field and determined that the alternating field can facilitate the transition of magnetization, specifically, by lowering the transitional field with the highest variation rate (33.73%).

Wave-Like Pseudo-Spin Valve Thin Film as a Biosensor

A magnetic biosensor using an anisotropic magnetoresistance effect based on a wave-like pseudo-spin valve is proposed. The wave-like structure formed trenches for attaching cells, which contain Fe3O4 magnetic nanoparticles by endocytosis, and subsequently altered the magnetic properties of pseudo-spin valve (10 nm Ti/8 nm CoFe/[4 nm Cu/4 nm CoFe]4/[4 nm Cu/8 nm CoFe]4/10 nm Ti). We measured the magnetic hysteresis loops via vibrating sample magnetometer (VSM) in three orthogonal directions. It was observed that devices with attaching cells show significant increases of the switching fields compared to the case without attaching cells when the external magnetic field is in parallel to the elongated trenches, considering an easy axis.

Magnetic Micro/Nano Structures for Biological Manipulation

Biomanipulation based on micro/nano structures is an attractive approach for biotechnology. To manipulate biological systems by magnetic forces, the magnetic labeling technology utilized magnetic nanoparticles (MNPs) as a common rule. Ferrofluid, well-dispersed MNPs, can be used for magnetic modification of the surface or as molds to form organized microstructures. For magnetic-based micro/nano structures, different methods to modulate magnetic field at the microscale have been developed. Specifically, this review focused on a new strategy which uses the concept of micromagnetism of patterned magnetic thin film with specific domain walls configurations to generate stable magnetic poles for cell patterning.