Screen-printed electrodes as impedimetric immunosensors for the detection of anti-transglutaminase antibodies in human sera

The concentration of anti-transglutaminase antibodies in human sera is an important analytical marker for the diagnosis of the autoimmune disorder celiac disease. In this work, an immunosensor for the electrochemical detection of anti-transglutaminase antibodies in human sera was developed. The immunosensor is based on the immobilization of transglutaminase onto screen-printed gold electrodes which were covered with a polyelectrolyte layer of poly (sodium-4-styrensulfonic acid). The antigen-antibody interaction was evaluated using an amplification step: incubation with peroxidase (POD)-labeled immunoglobulins and subsequent biocatalytic oxidation of 3-amino-9-ethylcarbazole (AEC). Changes in the interfacial properties of the sensor electrode were determined by electrochemical impedance spectroscopy (EIS). Impedance spectra could be fitted to a Randles equivalent circuit containing a constant phase element (CPE). Furthermore, it was shown that impedance measurements could be simplified by performing EIS at only two selected frequencies, without loss of reliability. Incubation of these disposable immunosensor chips with various anti-transglutaminase antibody concentrations resulted in changes in their charge transfer resistance (R_ct). Thereby, a calibration graph could be established. Finally, immunosensors were used for characterizing different human sera with respect to their anti-transglutaminase autoantibody concentration of the IgG and IgA type.