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

The biocatalyzed precipitation of an insoluble product produced on electrode supports is used as an amplification path for immunosensors. Faradaic impedance spectroscopy and chronopotentiometry are used as transduction methods to follow the precipitation processes. While Faradaic impedance spectroscopy leads to the characterization of the electron-transfer resistance at the electrode, chronopotentiometry provides the total resistance at the interfaces of the modified electrodes. An antigen monolayer electrode is used to sense the dinitrophenyl-antibody, DNP-Ab, applying an anti-antibody-HRP conjugate as a biocatalyst for the oxidative precipitation of 4-chloro-1-naphthol (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 intervals employed for the biocatalytic precipitation of (2). The electron-transfer resistances of the electrodes covered by the insoluble product (2) are derived from Faradaic impedance measurements, whereas the total electrode resistances are extracted from chronopotentiometric experiments. A good correlation between the total electrode resistances and the electron-transfer resistances at the conducting supports are found. Chronopotentiometry is suggested as a rapid transduction means, and the precautions for the application of chronopotentiometry in immunosensors are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.