Highly sensitive spin‐valve devices for chip‐cytometers

Abstract

The highly sensitive spin‐valve devices integrated with a microfluidic channel have been studied for cell counting in a chip‐cytometer. The presence or absence of a single magnetic bead was successfully detected by direct measurement of fringe fields emanating from magnetic beads using spin‐valve devices. The real‐time detection was also successfully confirmed by the direct measurement of magnetic fields generated from the magnetic beads passing an active sensing area of a spin‐valve device integrated with a microfluidic channel. Our results show the possibility of implementing a chip‐cytometer for biological applications using the highly sensitive spin‐valve devices integrated with a microfluidic device. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetization Manipulation of a Flexible Magnetic Sensor by Controlled Stress Application

“…After magnetic microbeads drop, almost zero Δ V is observed for the case of the reference cells, indicating that the magnetic beads on the reference cells are completely removed by the lift-off process. However, for the case of the sensing cells, Δ V is 35.4 mV at the zero external field, which is one of typical evidences for the existence of magnetic beads on the cell window area because the stray field from the beads affects magnetization reversal of the free layer 24 , 25 . Figure 5f shows normalized MR loops for the sensing cells in a field range of −75 Oe ≤ H ≤ 75 Oe before and after adding the microbeads.…”

Optimization of spin-valve parameters for magnetic bead trapping and manipulation

“…SVs are commonly used to sense beads [12][13][14][15], but sensing is not the focus of this study. Here we focus on an optimized SV design to trap and release individual superparamagnetic micro beads.…”

Dynamic micro-Hall detection of superparamagnetic beads in a microfluidic channel

“…So far, the research efforts in this direction have exclusively employed sensors based on metallic multilayer magnetoresistance technologies. 17,18,19,20,21,22 These sensors offer high sensitivity but often suffer from nonlinear responses, and more importantly, saturation at very low fields. On the other hand, micro-Hall devices have linear output and are not limited in the magnitude of the external magnetic fields that can be applied to magnetize SPM beads, which is advantageous for biodetection and necessary in magnetic separation.…”