Despina Davis

Magnetoresistance in Electrodeposited CoNiFe ∕ Cu Multilayered Nanotubes

Multilayered CoNiFe/Cu nanotubes were electrodeposited in nanoporous membranes under pulsed potential conditions from a single electrolyte. Giant magnetoresistance (GMR) measured with the current applied perpendicular to the plane of the layers was obtained at room temperature. This is the first demonstration of GMR in a nanotubular structure. We observed the value of the GMR at room temperature to be sensitive to the alloy layer deposition potential.

Fabrication and testing of a CoNiCu/Cu CPP-GMR nanowire-based microfluidic biosensor

Giant magneto resistance (GMR)-based microfluidic biosensors are used in applications involving the detection, analysis, enumeration and characterization of magnetic nano-particles attached to biological mediums such as antibodies and DNA. Here we introduce a novel multilayered CoNiCu/Cu nanowire GMR-based microfluidic biosensor. The current perpendicular to the plane of multilayers (CPP)-nanowires GMR was used as the core sensing material in the biosensor which responds to magnetic fields depending on the concentration and the flow velocity of bio-nano-magnetic fluids. The device was tested with different control solutions such as DI-water, mineral oil, phosphate buffered saline (PBS), ferrofluid, polystyrene superparamagnetic beads (PSB) and Dynabeads sheep anti-rabbit IgG. The nanowire array resistance decreased with an increase in the ferrofluid concentration, and a maximum 15.8% relative GMR was observed for the undiluted ferrofluid. The sensor was also responding differently to various ferrofluid flow rates. The GMR device showed variation in the output signal when the PSB and Dynabeads of different dilutions were pumped through it. When the tests were performed with pulsing potentials (150 mV and 200 mV), an increased GMR response was identified at higher voltages for PSB and Dynabeads sheep anti-rabbit IgG.

Electrodeposited, GMR CoNiFeCu Nanowires and Nanotubes from Electrolytes Maintained at Different Temperatures

Nanowires and nanotubes with modulated composition to realize a magnetoresistance effect were potentiostatically electrodeposited into alumina nanoporous templates. The multilayers were modulated between a Co-rich alloy and a Cu layer. The structure was characterized by electron microscopy. Deposits obtained from room temperature and 50°C electrolytes were nanowires, and a giant magnetoresistance (GMR) of up to 20% was observed. Chilling the electrolyte to 4°C resulted in nanotubes with a modulated structure. The current-potential behavior was examined with voltammetry and pulse transients. As expected, the cathodic current density increases with electrolyte temperature, although less obvious is the unfavorable anodic component, resulting during the transition between depositing the magnetic layer and a copper layer, which changes with time and differs with variable electrolyte temperature.

High Seebeck Coefficient BiSbTe Nanowires

Bismuth antimony telluride (BiSbTe) nanowires were electrodeposited at constant potentials into polycarbonate templates from a tartaric-nitric acid electrolyte. Optimum deposition potentials were obtained from polarization and compositional analysis. X-ray diffraction analysis showed a preferential (015) orientation for the nanowires. The Bi 2 Sb 0.6 Te 3 nanowire sample deposited at —150 mV showed a high Seebeck coefficient (S) of -630 μV/K.

Electrolyte Effect on Nanotubes Properties

The ability to electrodeposit magnetic (CoNiFeCu) and semiconductor (Bi2Te3) nanotubes was demonstrated from two different electrochemical systems. Electrodeposited multilayered CoNiFeCu/Cu nanotubes were fabricated by pulsing the applied potential. The electrolyte temperature affected the tube formation and the nanotubes giant magnetoresistance (GMR) saturation field. Both p/n-type Bi2Te3 alloy nanotubes were deposited under constant potential from different electrolyte concentrations and component ratios. We report the Seebeck coefficient measurement method for Bi2Te3 alloy nanotubes obtained by electrodeposition.

Microfabrication of nanowires-based GMR biosensor

This study focuses on the development of current-perpendicular-to plane (CPP) Giant Magnetoresistance (GMR) of CoNiCu/Cu multilayered nanowire based microfluidic sensors for the detection of magnetic nanoparticles and fluids. The visible measurable variations in electrical voltage due to changes in external magnetic field are later to be monitored in microfluidic biosensor for the detection of toxicants in cells. An early prototype device was fabricated and tested using both an aqueous nonmagnetic medium (water) and a commercially available ferrofluid solution. A magnetic field of 0.01T caused a resistance change of 1.37% for ferrofluid, while a 1.1% GMR was recorded for the water baseline.

Nanowire-GMR Integrated Microfluidic Biosensor

Nanowires based GMR is ideal to be integrated in microfluidic devices due to its efficient detection of sensitive magnetic fields. Nanowire based GMR microfluidic sensor is used to detect different fluids based on their magnetic behavior. This paper demonstrates the fabrication and testing of nanowire based GMR biosensors with four different control solutions: 1) DI-water, 2) Phosphate Buffered Saline (PBS), 3) polystyrene superparamagnetic beads, and 4) commercially available magnetic Dynabeads. The device is fabricated in PDMS by using a lithographically patterned silicon wafer as the mold. The nanowire based GMR material, 3 mm by 3 mm in size, is inserted inside the PDMS close to the channel during the fabrication. The channel in the PDMS substrate is sealed by bonding it to a glass plate using Reactive-Ion-Exchanger (RIE). GMR device is tested potentiostatically using a computer controlled function generator (Solatron, SI 1287). A highest resistance of 0.748 Ω. is recorded for the sensor, in the absence of magnetic field. A resistance change of 0.6% is obtained in the presence of a magnetic field (B = 0.035T) between water and polystyrene superparamagnetic beads when pumped through the microchannel. The sensor showed a resistance difference of 0.31% between 1X diluted PBS and 100X diluted dynabeads, in the presence of a constant magnetic field of 0.035T. This characterization would be useful in the development of a BioMEMS sensor using nanowire based GMR.Copyright