Detection of Nitric Oxide on Carbon Electrode Modified with Ionic Polymers and α-Cyclodextrin

Abstract

To obtain basic information for the development of high performance electrochemical NO sensor for biological systems, performance of carbon electrodes (based on mechanical pencil leads) covered with three-layered films consisting of cationic polymer, a sieving material for NO (α-cyclodextrin, α-CD), and anionic polymer (Nafion) was investigated in vitro. We have anticipated that cationic and anionic polymer films effectively discriminate ionic species present in biological systems and that α-CD layer placed between ionic polymer films avoids charge neutralization of polymer films and concentrates NO near electrode surface by reversible sieving effects. Among cationic polymers investigated, poly(diallyldimethylammonium chloride) (PDDA) formed a film more stable than poly(ethyleneimine) (PEI) and poly(allylamine hydrochloride) (PAH). By cyclic voltammetry (CV) measurements, an electrode covered with PDDA /α-CD/ Nafion (typical thickness: 20, < 1, and 30 µm, respectively) showed higher NO oxidation current than a bare electrode, and little oxidation currents for materials present in living body, such as ascorbic acid, uric acid, dopamine hydrochloride, and sodium nitrite. Films prepared by drying solutions containing polymer and α-CD at 80°C for 5 min were stable at least for 80 min during differential pulse voltammetry (DPV) measurements with intermittent NO bubbling in a physiological saline solution called Krebs-Henseleit (KH).