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.

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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.