AN APPROACH TO CONDUCTOMETRIC IMMUNOSENSOR BASED ON PHTHALOCYANINE THIN-FILM

A new approach to conductometric biosensors utilizing iodine-sensitive phthalocyanine thin films has been proposed. The excellent sensitivit y of the tetra-tert-butyl copper phthalocyanine (ttb-CuPc) to free iod ine was used for the first time to detect a peroxidase-initiated react ion in an aqueous medium. To minimize the interfering effect of aqueou s electrolytes on the impedance responses of the ttb-CuPc film itself, Au/Cr interdigitated planar electrodes bearing ttb-CuPc thin films we re protected with hydrophobic gas-permeable membranes, namely thermall y evaporated calixarene or plasma polymerized hexamethyldisiloxane fil ms. Impedance spectroscopy data were analyzed in order to define the o ptimal operating frequency. An enzyme sensor with peroxidase immobiliz ed in a cross-linked albumin matrix was tested. Its impedance response s were studied under variation of the substrate concentration, pH, ion ic strength and buffer capacity. These results were used to define con ditions for peroxidase-linked immunoassay in subsequent tests. With th e developed sensor, concentrations of IgG in 0.2-2 mu g/ml range were measured in a competitive mode with satisfactory accuracy. The detecti on of Ige in both test solutions and blood serum samples has been demo nstrated. (C) 1998 Elsevier Science S.A. All rights reserved.