Label-free electrochemical impedance spectroscopy biosensor for the determination of human immunoglobulin G

A simple and sensitive biosensor was developed for the determination of human immunoglobulin G (IgG). Protein A was employed as molecular receptor and electrochemical impedance spectroscopy (EIS) was used as detection technique. The biosensor was obtained by self-assembling protein A on a gold electrode. The surface morphology of the self-assembled layer before and after interaction with IgG was studied by atomic force microscopy. Protein A bound specifically to the Fc portion of IgG, and this caused a change in the resistance of the interfacial electron transfer when using a ferrocyanide redox couple as a probe. The increase of the resistance of the electron transfer was linearly related to the concentration of IgG in the range from 10 ng.mL(-1) to 1.0 mu g.mL(-1), with a detection limit of 5 ng.mL(-1). The work demonstrates that protein A is a versatile matrix for the immobilization of antibodies.