Development of capacitance based immunosensors on mixed self-assembled monolayers

The construction and characterisation of a capacitance based immunosensor on mixed mercaptohexadecanoic acid and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-caproyl biotinyl self-assembled monolayers on gold are reported. Immobilisation of IgG antibodies was achieved using the strong non-covalent bond formed between Neutravidin and biotin to tether anti-human haemoglobin goat IgG to the mixed monolayers. Analysis of sensor construction and of the functional immunosensors was characterized via physical techniques, including quartz crystal microbalance, and atomic force microscopy for surface topographical measurement. Sensor assembly and the binding affinity of immobilised antibodies were independently determined using [125I]-tagged components. Finally, the electrochemical properties of partially constructed and fully functional immunosensors were analysed by electrochemical impedance spectroscopy in a ferricyanide mediated system. The haemoglobin sensors show a linear response of the imaginary component of impedance (Z″) across a wide range of concentrations, from 10−10 (according to Fig. 8, linearity is restricted over the concentration range 10−8 to 10−6 M haemoglobin), at the lower range of frequencies examined.