Functionalization of micro-Hall effect sensors for biomedical applications utilizing superparamagnetic beads

This paper aims to meet demands of affordable and reliable analytical tools for detection, identification and quantification of DNA and other biomolecules. This work has two main objectives: (i) fabrication of Hall sensors that are compatible, with biological environment via a waterproof sensor passivation layer, insulation of electrical contacts, providing an interface for biomolecules, and suitable packaging; (ii) selection of highly selective biomolecular interactions for attachment of beads via specific target molecules. Practical applications of such sensors will depend on the optimal choice with regard to the specific combination of biochemical interactions securing immobilization of the microbeads to the sensor only when the selected target molecule is present in the analyte. Several variations of potentially practical schemes for immobilization have been reported in various contexts. In this study, this aspect was investigated for InSb micro-Hall sensors. The key issues identified were: the thiol-gold interaction for immobilization (direct or indirect) of probe molecules to the sensor surface; utilization of biochemical bonding between small molecules like biotin and large biomolecules like proteins or DNA; and finally extremely specific hybridization processes between complementary DNA fragments.