Exchange-Biased AMR Bridges for Magnetic Field Sensing and Biosensing

Abstract

We introduce magnetic field sensor bridges that are formed by combinations of stripes of an exchange-pinned magnetic stack displaying anisotropic magnetoresistance. We present a systematic overview on how the stripe geometries can be combined to form sensor bridges with a scalable signal and how these can be tailored towards detection of external magnetic fields and of magnetic beads over or tethered to the sensor surface. Particular attention is given to the case where the beads are magnetized by the sensor self-field due to the bias current passed through the sensor, which is interesting for magnetic bead sensing and where the static and dynamic magnetic bead response can be monitored in the 2nd harmonic sensor response to an oscillating bias current. The recent literature on applications of these sensors for detection of magnetic fields and of the dynamic and static response of magnetic beads in suspension and attached to the sensor surface is reviewed as well as the use of the sensors for magnetic biosensing in volumeand surface-based formats. We illustrate that the sensors can be flexibly designed and applied for a number of sensing applications with sensitive detection of magnetic fields down to the nT range.Index Terms-Magnetoresistive sensor, planar Hall effect, magnetic field sensor, magnetic biosensor.

A new dimension for magnetosensitive e-skins: active matrix integrated micro-origami sensor arrays

“…2g and Supplementary Fig. 5a ) 50 , 51 . The AMR stripe elements are interconnected by Au pads and rotated by 45° to the bias field during deposition, adjusting the sensor bridge to its maximum sensitivity (Left inset in Fig.…”

Magnetoresistive Biosensors for Direct Detection of Magnetic Nanoparticle Conjugated Biomarkers on a Chip

“…45 However, biolabeling techniques of MNPs provide a favorable basis for the development of magnetic biosensors. Therefore, some welldeveloped methods for magnetic¯eld detection have been used in biosensing applications, including (i) magnetoresistive (MR) methods such as anisotropic magnetoresistance (AMR), [46][47][48][49][50][51][52] giant magnetoresistance (GMR), [53][54][55][56][57] tunneling magnetoresistance (TMR), 58,59 giant magnetoimpedance (GMI) [60][61][62][63] and (ii) nonMR methods such as those involving the use of a°ux gate sensor, Hall sensor and superconducting quantum interference device (SQUID). [64][65][66][67][68][69] Several magnetic¯eld sensors have been used in biodiagnostics, but the drawbacks of large size, low sensitivity, or high power consumption limited their use in practical applications.…”

“…Hien et al developed a DNA probe targeting system that could be replaced after testing. 46 The DNA probe was magnetically labeled with paramagnetic beads and then immobilized on a card substrate. The DNA magnetic beads were detected with a limit of 4.5 pmol for a target DNA by using an AMR biosensor with a Wheatstone bridge con¯guration, 47 which o®ers a sensitivity that is almost two times higher than that of a single AMR sensor.…”

Ultrasensitive Magnetic Field Sensors for Biomedical Applications

“…Recently, AMR-based microstructures [225][226][227] were proposed for magnetic beads detection, but, nowadays, because of the low change of resistivity [227] (around 2%), magnetoresistive biosensors based on GMR and TMR are more popular. For detailed information about exchange-biased AMR sensors tailored for magnetic bead sensing in lab-on-a-chip systems, we refer to the overview written by Hansen [228]. Biosensors based on TMR are also good candidates for biomedical detection due to the ability to detect low magnitude magnetic fields.…”