Practical Hall effect sensors for biomedical instrumentation - 'horses for courses'

There is intense worldwide activity in the development of instrumentation for medical diagnosis and bioscreening based on biological labeling and detection of superparamagnetic particles. This paper describes recent results of a systematic study on the fabrication of high sensitivity micro and nano-Hall devices for biomedical applications using a wide range of materials. Issues related to the ease of fabrication, scalability, magnetic field sensitivity and functionalization will be discussed. The extensive variety of materials available for Hall sensor fabrication offers a highly flexible, 'tailor-made' route for the development of instrumentation for detection and analysis of biological labeled superparamagnetic particles. The devices described in this paper (InSb linear arrays, InAs 'bridge-type' sensor, bismuth thin film nano-Hall sensor, GaN/AlGaN 2DEG sensor) were incorporated into the measurement system as described and successfully used to detect magnetic beads ranging between 0.12 to 2.8 microns in diameter. The electrical characteristics of novel micro-Hall sensors fabricated using GaN/AlGaN 2DEG heterostructures and InAs bridge structures are described. Methods for immobilization of DNA and other biomolecules onto the surfaces of these devices will also be discussed.