Tzong-Rong Ger

Cell patterning using microstructured ferromagnetic thin films

Magnetic cell patterning is demonstrated through controlling the micromagnetic states in microstructured ferromagneticthin films. The number of magnetic nanoparticles entering the cells by endocytosis can be determined by magnetophoresis experiment and is found to be dependent of the cocultured extracellular magnetic nanoparticles concentrations. In zigzag magnetic films the effects of cell patterning differ for magnetic films at as-deposited state and at remanent states after applying fields in different directions. Remanent states of concentric rings are proposed for cell patterning. Cells can be arranged at any positions in sequence by selectively changing the magnetic field directions.

A permalloy zigzag structure based magnetic bio-sensor

A magnetic fluid consisting of Fe3O4 magnetic nanoparticles is embedded inside cells by intracellular uptake. A micro-fabricated magnetic zigzag-shaped surface structure is studied for use as a biosensor. We have developed a MOKE magnetometer based methodology to measure the different hysteresis loop signals between cells with and without being placed on zigzag sensors. Adding the magnetic cells on the structure decreases the coercivity from the magneto-optical Kerr effect (MOKE) signal of zigzag magnetic thin films because of the magnetic properties of superparamagnetic nanoparticles. The magnetoresistance measurement observed is that the switching fields of the zigzag structure with magnetic cells are significantly increased compared to the case without cells in the hard axis of the external field applied.

Compare analysis for the nanotoxicity effects of different amounts of endocytic iron oxide nanoparticles at single cell level.

Developing methods that evaluate the cellular uptake of magnetic nanoparticles (MNPs) and nanotoxicity effects at single-cellular level are needed. In this study, magnetophoresis combining fluorescence based cytotoxicity assay was proposed to assess the viability and the single-cellular MNPs uptake simultaneously. Malignant cells (SKHep-1, HepG2, HeLa) were incubated with 10 nm anionic iron oxide nanoparticles. Prussian blue stain was performed to visualize the distribution of magnetic nanoparticles. MTT and fluorescence based assay analyzed the cytotoxicity effects of the bulk cell population and single cell, respectively. DAPI/PI stained was applied to evaluate death mechanism. The number of intracellular MNPs was found to be strongly correlated with the cell death. Significant differences between cellular MNP uptake in living and dead cells were observed. The method could be useful for future study of the nanotoxicity induced by MNPs.

Anti-integrin and integrin detection using the heat dissipation of surface plasmon resonance

We verified that the heat dissipation of surface plasmon resonance can be measured using photothermal deflection method. The maximum value of photothermal deflection corresponded to the occurrence of surface plasmon resonance. The detection of anti-integrin and integrin biomolecules that exhibit specific binding was demonstrated using this technique. From our experimental results it shows that the photothermal deflection method can be used to obtain the surface plasmon resonance angles and angle shift.

Detection of Magnetically Labeled Cells Using Wavelike Permalloy Nanowires

Permalloy nanowires of 150, 300, 500, and 800 nm widths deposited onto wavelike silicon trenches were designed as single-cell sensing devices. Magnetoresistance curves before and after attaching a single magnetic cell on the nanowires were measured when magnetic fields were applied in various directions. It was observed that the highest sensitivity (27%) in switching field variation after a cell was attached can be obtained when the field was applied perpendicular to the plane of the 150-nm-wide nanowire. The highest sensitivity (25.5%) in magnetoresistance ratio variation occurred in the 800-nm-wide nanowire in the same field direction.

Angular arrangements of triangular fins for controlling the magnetization processes in permalloy rings

The influences of triangular fins’ positions on controlling the magnetization processes are investigated. It is observed experimentally that when the included angle between the triangular fins and the field direction is 15° or 30°, the magnetization reversals are repeatable in the sweep-up and sweep-down processes, and the magnetization processes are controllable. In contrast, when the included angle between the triangular fins and the field direction is 45° or 60°, the magnetization reversals are unrepeatable and random in the sweep-up and sweep-down processes. Magnetization reversal can only be controlled when positions of the triangular fins are close to the original nucleation regions of the rings. When triangular fins are away from the original nucleation regions, two kinds of magnetization reversals randomly occur without being controlled by the artificial nucleation sites, and the triangular fins thus lose their control ability.

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.

Wavy ferromagnetic device as single cell detection

We demonstrate a design of using a wavy permalloy thin film as a cell sensing device for the purpose of single magnetic cell detection. The magnetoresistance curve (MR curve) differs according to the single magnetic cell attached to the surface. By analyzing the MR curves, we can determine the sensing capability of the permalloy magnetic film device. Our results indicate that the sensitivity of the permalloy film sensing devices with wavy surface is much higher than the devices with flat surface. When a single magnetic cell is captured by the wavy surface of the permalloy film, the switching field of the film increase which is caused by the stray field of the magnetic cell. We discover that the highest sensitivity occurs when the direction of the magnetic field is along the Z-axis, and there is significant potential for the application of cell detection.

Surface Roughness Effects on Magnetization Reversal of Magnetic Ring Elements

The effect of surface roughness on magnetoresistance of permalloy ring structure is investigated. Microstructured permalloy rings with surface roughness varying from 4.2 to 21 nm were fabricated using electron beam lithography and a chemical etching process. It is found experimentally that the first and second nucleation fields decrease obviously with the surface roughness increasing, and the field range for the flux-closure state is not associated with surface roughness. The results indicate that surface roughness in permalloy ring structure is an important factor that influences the magnetic behaviors of the ring. This result can provide important information for future designs of ring-shaped magnetic devices.

Thermoelectric Property of Nickel Nanowires Enhanced by Resistance

In this paper, we report a method to create nickel nanowires with various resistances, as well as its thermoelectric measurement. We found out that the various resistances can directly improve the thermoelectric effect. The resistance can reduce the thermal conductivity and would significantly increase the Seebeck voltage. The thermoelectric voltage of the nanowire with the highest resistance is found to be 4.5 times higher than the nanowire with the smallest resistance. Under a temperature difference of 10.068 K between the hot side and cold side, the generated electrical motive force can reach 0.791 mV. Besides, the nickel nanowire possesses overall better thermoelectric efficiency than the Au nanowire, under same temperature difference of 10.068 K, and the nickel nanowire yields a 4.24 times higher voltage than Au nanowire.