Abstract

The impedance spectroscopy was employed to follow the different steps of the immunosensor fabrication and the electronic transduction for the detection of the specific rabbit antigen IgG. A mixed amphiphile (octadecylamine)-antibody Langmuir-Blodgett (LB) film was structured at the air-water interface and transferred onto an octaclecyl thiol (ODT) modified silver electrode. Impedance spectroscopy allows one to model the different layers with equivalent electrical circuits. A real probing of the ODT self-assembled monolayer (SAM) was done: electrical defects were found in the ODT SAM and they disappeared after deposition of the LB film. It can be suggested that these defects were suppressed by inclusion of octadecylamine (ODA) in the ODT layer. The total impedance of the mixed LB film increased in the presence of an increasing concentration of specific antigen. The equivalent circuit shows a decrease of the capacitance of the LB bilayer and an increase of its resistance. Such a structured building-up including biomolecules leads to a reproducible immunosensor, allowing detection of the specific antigen in the range from 10 ng ml(-1) to 1200 ng ml(-1).

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