A new method based on a biochemical binding system is developed for de
tecting the presence and measuring the concentration of a definite ana
lyte in fluids. The conductometric scheme of detection has been employ
ed for detection of the binding reaction of immunoglobulins. Two ident
ical pairs of gold interdigitated electrodes deposited on the insulati
ng solid support have been used as a detector. An electrically conduct
ing polymer, namely polyaniline, has been proposed as a label for immu
nosensor development. A set of water-soluble forms of polyaniline with
different molecular weights and oxidation levels have been prepared b
y chemical oxidation of aniline and characterized using gel-permeation
chromatography. The acceptability of different kinds of polyaniline,
and the selectivity and sensitivity of sensor response have been studi
ed. The method of antibody detection in competitive electroimmunoassay
has been developed. The lowest antigen concentration which may be det
ected in the competitive mode was found to be about 500 ng/ml. The res
ults of impedance spectroscopy measurements obtained for different sta
tes of the electrodes are analyzed in order to clarify the mechanism o
f the sensor response.