IMPEDANCE ANALYSIS OF SI/SIO2 STRUCTURES GRAFTED WITH BIOMOLECULES FOR THE ELABORATION OF AN IMMUNOSENSOR

Impedance measurements on Si/SiO2 structures grafted with biomolecules have been compared by using an electrochemical cell and a mercury probe. A grafting of octadecyldimethyl(dimethylamino) silane has been performed on thin (80 Angstrom) thermal oxides, yielding dense and well-structured monolayers of molecules. Their thicknesses have been derived from capacitance measurements and compared with the known length of the molecule. The results seem to indicate that an electrolytical contact is more appropriate than the contact of the mercury probe. The impedance measurements with the mercury probe have, however, permitted to establish the basis of an electrical model of the membrane of an impedimetric immunosensor based on an Si/SiO2 structure.