Optimisation of Hall cross devices towards magnetic particle counting
type: CreativeWork
description: The magnetic detection of magnetically labelled disease biomarkers from a sample of bodily fluid presents an interesting architecture for a disease diagnostic device. Many advantages are offered over conventional optical labelling and detection techniques, including reduced background signals and sample pre-processing requirements due to the lack of magnetically responsive material in biological samples, as well as enhanced control over various steps of the assay protocol as magnetic labels may be actuated remotely via the application of magnetic fields. In this thesis, Hall cross sensors are explored for the detection and enumeration of large numbers of magnetic particles for applications in magnetic immunoassays. The response of a Hall cross to a magnetic particle is directly proportional to the stray field of that particle averaged over the active area of the cross. As the active area size increases relative to the particle size, due to the solenoidal nature of the particle’s stray field, this average tends towards zero. As a result, large area Hall sensors suffer from low single particle signals, limiting device resolution. In addition, the Hall response is found to be highly inhomogeneous as a function of particle position, limiting the certainty with which particles may be counted. Hall cross sensors for which the active area size match the particle size produce a much larger response and can be used detect the binary presence or absence of a particle, thus resolving issues with both signal strength and homogeneity. However, dense arrays of individually contactable sensors must be fabricated to detect meaningful numbers of particles, limiting their usefulness. This work focuses on the optimisation of large area Hall cross sensors towards the goal of counting large numbers of magnetic particles simultaneously with improved resolution and measurement uncertainty. It is hypothesised that the inclusion of perforations within the active area of such devices could m…
abstract: The magnetic detection of magnetically labelled disease biomarkers from a sample of bodily fluid presents an interesting architecture for a disease diagnostic device. Many advantages are offered over conventional optical labelling and detection techniques, including reduced background signals and sample pre-processing requirements due to the lack of magnetically responsive material in biological samples, as well as enhanced control over various steps of the assay protocol as magnetic labels may be actuated remotely via the application of magnetic fields. In this thesis, Hall cross sensors are explored for the detection and enumeration of large numbers of magnetic particles for applications in magnetic immunoassays. The response of a Hall cross to a magnetic particle is directly proportional to the stray field of that particle averaged over the active area of the cross. As the active area size increases relative to the particle size, due to the solenoidal nature of the particle’s stray field, this average tends towards zero. As a result, large area Hall sensors suffer from low single particle signals, limiting device resolution. In addition, the Hall response is found to be highly inhomogeneous as a function of particle position, limiting the certainty with which particles may be counted. Hall cross sensors for which the active area size match the particle size produce a much larger response and can be used detect the binary presence or absence of a particle, thus resolving issues with both signal strength and homogeneity. However, dense arrays of individually contactable sensors must be fabricated to detect meaningful numbers of particles, limiting their usefulness. This work focuses on the optimisation of large area Hall cross sensors towards the goal of counting large numbers of magnetic particles simultaneously with improved resolution and measurement uncertainty. It is hypothesised that the inclusion of perforations within the active area of such devices could m…
author: Herbert, Holly
language: eng
keywords: Hall cross devices, magnetic materials
license: https://www.repository.cam.ac.uk/bitstreams/9d7267fb-f706-417e-9c18-45ea3352ceef/download
license: https://www.rioxx.net/licenses/all-rights-reserved/
date published: 2022-12-31
date modified: 2026-07-22T22:23:56Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.104759