Chronopotentiometry and Faradaic impedance spectroscopy as methods for signal transduction in immunosensors

The biocatalyzed precipitation of an insoluble product produced on electrod e supports is used as an amplification path for immunosensors. Faradaic imp edance spectroscopy and chronopotentiometry are used as transduction method s to follow the precipitation processes. While Faradaic impedance spectrosc opy leads to the characterization of the electron-transfer resistance at th e electrode, chronopotentiometry provides the total resistance at the inter faces of the modified electrodes. An antigen monolayer electrode is used to sense the dinitrophenyl-antibody, DNP-Ab, applying an anti-antibody-HRP co njugate as a biocatalyst for the oxidative precipitation of 4-chloro-1-naph thol (1) by H2O2 to yield the insoluble product benzo-4-chlorohexadienone ( 2). The amount of the precipitate accumulated on the conductive support is controlled by the concentration of the analyte-antibody and the time interv als employed for the biocatalytic precipitation of (2). The electron-transf er resistances of the electrodes covered by the insoluble product (2) are d erived from Faradaic impedance measurements, whereas the total electrode re sistances are extracted from chronopotentiometric experiments. A good corre lation between the total electrode resistances and the electron-transfer re sistances at the conducting supports are found. Chronopotentiometry is sugg ested as a rapid transduction means, and the precautions for the applicatio n of chronopotentiometry in immunosensors are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.