Towards the development of an electrochemical biosensor for hCGβ detection

The free beta subunit of human-chorionic-gonadotropin (hCGβ) is critical for various aspects of human health. Detection and quantification of this protein are essential during pregnancy as it provides clinicians valuable information regarding the progress of a pregnancy and the health of a foetus. Furthermore, it can be used as a biomarker for gestational trophoblastic disease (GTD), germ cell tumours and some non-trophoblastic gynaecological cancers and common epithelial tumours. Monitoring hCGβ levels is particularly important for patient treatment monitoring and relapse detection especially in GTD. This paper presents an investigation of the characteristics of the first two stages necessary for the development of a bio-impedance hCGβ sensor, using impedance spectroscopy and commercially available microelectrodes. Additionally, electrical equivalent circuit models based on the experimental results of these stages are presented. The biosensor is based on the formation of stable antibody–antigen complexes on golden microband electrodes covered with a layer of a self-assembled monolayer (SAM) or with both SAM and protein G. The preliminary results and analysis relate the interfacial processes and physical structure of the sensor to its electrical behaviour. Finally, preliminary results obtained from the sensor without protein G, which strongly indicate hCGβ detection, are also presented.