Hao-Ting Huang

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.

Cells positioning using magnetic domain walls of ferromagnetic zigzag thin film

Magnetic cell positioning is demonstrated by controlling the magnetic domain walls in ferromagnetic zigzag thin films. Magnetophoresis experiment is performed to determine the number of magnetic nanoparticles that enter the cells by endocytosis. It is observed that in the zigzag structure with larger wavelength the magnetic cells are better aligned at the vertices.

Wheatstone bridge giant-magnetoresistance based cell counter.

A Wheatstone bridge giant magnetoresistance (GMR) biosensor was proposed here for the detection and counting of magnetic cells. The biosensor was made of a top-pinned spin-valve layer structure, and it was integrated with a microchannel possessing the function of hydrodynamic focusing that allowed the cells to flow in series one by one and ensured the accuracy of detection. Through measuring the magnetoresistance variation caused by the stray field of the magnetic cells that flowed through the microchannel above the GMR biosensor, we can not only detect and count the cells but we can also recognize cells with different magnetic moments. In addition, a magnetic field gradient was applied for the separation of different cells into different channels.

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.

Investigation of the magnetization process in a three-dimensional curled up structure

The results of our study provide the magnetic switching behavior of a curled up Ni magnetic structure in comparison to the initially flat magnetic film. We used e-beam lithography, an electron beam evaporation system, and a wet etching technique to fabricate the magnetic curled up structure. Because of the different thermal expansion coefficients of the film materials, the released stress causes the structure to be curled up after the wet etching process. We study the properties of the submicron magnetic structure via magnetoresistance measurements. Magnetization reversal properties are strongly affected by the curl up process. The magnetoresistance of single Ni flat structures is based upon the anisotropic magnetoresistance. The structure stress release during the curl up process causes the magnetic switching to be slightly higher than that of a flat thin film. It is observed experimentally by differences in the slope of the reversal curves that a three-dimensional curled up structure comes out of a meta...

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.

Controllable Magnetization Processes Induced by Nucleation Sites in Permalloy Rings

Different arrangements of notches as nucleation sites are demonstrated experimentally and numerically to effectively control the magnetization processes of permalloy rings. In the ring with notches at the same side with respect to field direction, two same-helicity vortex domain walls in the onion state lead to two-step switching going through flux-closure state; in the ring with diagonal notches two opposite-helicity vortex domain walls lead to one-step switching skipping flux-closure state. The switching processes are repeatable in contrast to rings without notches where helicites of two vortex domain walls are random so the switching processes can not be controlled.