An immunosensor for haemoglobin based on impedimetric properties of a new mixed self-assembled monolayer

A novel impedimetric immunosensor for the detection of haemoglobin has been developed by mixed self-assembled monolayers on Au. First, a mixed self-assembled monolayer (SAMs) consisting of 1,2 dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-(biotinyl) (biotinyl-PE) and 16-mercaptohexadecanoic acid (MHDA) on gold electrodes was studied. The conformational properties of the SAMs were characterised by cyclic voltammetry and impedance spectroscopy. After blocking non-specific binding sites in the mixed monolayer using non-specific IgG, neutravidin was used to bind to biotinyl sites present in the mixed monolayer. Finally, biotinylated anti-haemoglobin IgG was immobilised to the tethered neutravidin. The membrane resistance R_m, obtained from the assembly, decreased gradually after the addition of non-specific IgG, neutravidin and anti-haemoglobin to the monolayer. This decrease could be attributed to a rearrangement in the structure of the SAMs. The detection of antibody–antigen reaction demonstrates that the potentiometric immunosensor exhibited high sensitivity and a detection limit of 20 ng/ml (approximately 0.3 nM).