Giant Magnetoresistance Sensors. 1. Internally Calibrated Readout of Scanned Magnetic Arrays

Abstract

This paper describes efforts aimed at setting the stage for the application of giant magnetoresistance sensor (GMRs) networks as readers for quantification of biolytes selectively captured and then labeled with superparamagnetic particles on a scanned chip-scale array. The novelty and long-range goal of this research draws from the potential development of a card-swipe instrument through which an array of micrometer-sized, magnetically tagged addresses (i.e., a sample stick) can be interrogated in a manner analogous to a credit card reader. This work describes the construction and testing of a first-generation instrument that uses a GMR sensor network to read the response of a "simulated" sample stick. The glass sample stick is composed of 20-nm-thick films of permalloy that have square or rectangular lateral footprints of up to a few hundred micrometers. Experiments were carried out to gain a fundamental understanding of the dependence of the GMR response on the separation between, and planarity of, the scanned sample stick and sensor. Results showed that the complex interplay between these experimentally controllable variables strongly affect the shape and magnitude of the observed signal and, ultimately, the limit of detection. This study also assessed the merits of using on-sample standards as internal references as a facile means to account for small variations in the gap between the sample stick and sensor. These findings were then analyzed to determine various analytical figures of merit (e.g., limit of detection in terms of the amount of magnetizable material on each address) for this readout strategy. An in-depth description of the first-generation test equipment is presented, along with a brief discussion of the potential widespread applicability of the concept.Magnetoresistance is defined as the change in the resistance of a material in response to an externally applied magnetic field (H app ). All conductors show a small level of magnetoresistance, but normally not more than 1%. However, as discovered in 1988, [1][2][3] some multilayer systems exhibit a change in resistance of up to 80%. 4 This phenomenon is based upon the quantum mechanical exchange coupling between thin layers of magnetic materials that are separated by comparably thin layers of nonmagnetic materials 5 and is known as giant magnetoresistance. With these materials, an increase in H app induces a decrease in resistance. Since 1988, giant magnetoresistance sensors (GMRs) have become one of the most heavily used tools for the detection of magnetic fields. While almost universally employed as compact, high-density, and highspeed read heads in computer hard drives, 6 GMRs have also found specialty applications in several other areas, 4,7,8 including antilock brakes, 9 magnetic imaging, 10 and galvanic isolators. 11Several laboratories have begun to transition GMRs from the data storage domain to that of the bioanalytical sciences.12-24 The goal is to create miniaturized devices based on magnetic labeling concepts by taking advantage o...

Giant Magenetoresistive Sensors. 2. Detection of Biorecognition Events at Self-Referencing and Magnetically Tagged Arrays

“…The magnitude of the GMR sensor response is then related to the amount of magnetically labeled bioanalyte selectively coupled to each address. This strategy, as noted earlier, 23 has two important outcomes. First, it moves GMRs from a single-use format in a solid-phase capture assay to one in which the same GMR network can be employed repeatedly to read a large number of addresses on one or more sample sticks.…”

“…Second, and of comparable importance, this concept provides a pathway to incorporate thin films of magnetic materials as addresses that function as on-stick references. On-stick references provide a means not only to compensate for the dependence of the GMR response to small changes in the separation between the magnetic sample and the GMR, 23,24 but also to internally calibrate the response at each sample address. 23 This paper uses the reaction scheme illustrated in Figure 1 to create a biotin-capture substrate and the subsequent selective extraction of superparamagnetic particles (MPs) coated with a layer of streptavidin (SA).…”

“…Scanning Readout of Sample Stick. The design of the probe station and the mechanics of aligning and reading the sample stick, which is detailed in the companion paper, 23 provides a reliable mechanism to scan the GMR across the sample stick ( Figure 4) and parallel to H app in accordance with Figure 6. That is, the GMR sense resistors pass directly under the sample stick at a separation of ∼50 µm.…”

Giant Magnetoresistance Sensors Based on Ferrite Material and Its Applications

“…Nordling et al [25] have used the Wheatstone bridge to develop integrated GMR sensors. This system consists of four GMRs that are integrated into serpentine, as shown in Figure 6.…”

Linearization strategies for high sensitivity magnetoresistive sensors

“…Non destructive testing, either for flux leakage detection for packaging control [12] or metal surface cracks scanning [13,14], is another relevant area where MR sensors are used. Magnetic biosensors based on MR technology used to detect surface binding reactions of biological molecules labelled with magnetic particles, is an emerging field providing key advantages for both research and clinical settings, as sensors can be arrayed and multiplexed to perform complex protein or nucleic acid analysis in a single assay with full scalable IC integration capability, making it appealing for point-of-care (POC) applications along with lab-on-chip systems [15][16][17][18][19][20][21].…”