Abstract: The label-free amperometric detection of a rabbit IgG antigen by an anti-rabbit IgG antibody is achieved by observing the electrochemistry at a glassy carbon electrode modified with antibody entrapped in an electrodeposited polypyrrole membrane. In a flow injection apparatus the electrode is pulsed between -0.2 and +0.4 V versus Ag/AgCl. The pulsing of the electrode switches the polypyrrole membrane between the oxidized and reduced states. When antigen is injected into the flow stream a change in current is observed at the electrode despite the antigen or antibody being redox inactive at the potentials employed. It is proposed that this current is due to a change in the flux of ions into and out of the polypyrrole matrix during a pulse when the poly-anionic antigen is present. The immunoreaction was reversible because the 200 ms pulse at each potential was too short to allow secondary bonding forces (hydrogen bonding and hydrophobic forces) which are responsible for the strength of the antibody-antigen complex to be established. The consequence of the reversibility of the antigen-antibody binding is a low apparent affinity constant but an easily regenerated recognition interface.

Abstract: The development of a sulfite biosensor based on the immobilization of sulfite oxidase (SOD) in electrodeposited polytyramine is described. Electropolymerization of polytyramine and simultaneous immobilization of SOD on platinized glassy carbon (GC/Pt) were performed in an aqueous solution of 0.1 M tyramine containing SOD. The sulfite biosensor constructed with five voltammetric sweep cycles showed a sensitive response to sulfite with a linear calibration curve in the concentration range 0.002-0.3 mM sulfite, slope 2.70 µA l mmol-1, and detection limit 0.001 mM sulfite (S/N = 3). Deposited polytyramine enhanced the selectivity of the biosensor by eliminating direct oxidation of sulfite and other interfering agents at the electrode. The biosensor was applied for the determination of sulfite in various types of wine samples, and the results obtained are in agreement with those using an AOAC method.