Thin-film modified electrodes with reconstituted cellulose-PDDAC films for the accumulation and detection of triclosan

A strategy for the formation of thin reconstituted cellulose films (pure or modified)) with embedded receptors or embedded ion-selective components is reported. Cellulose nanofibril ribbons from sisal of typically 3−5 nm diameter and 250 nm length are reconstituted into thin films of typically 1.5−2.0 μm thickness (or into thicker free-standing films). Cellulose and cellulose nanocomposite films are obtained in a simple solvent evaporation process. Poly-(diallyldimethylammonium chloride) or PDDAC is readily embedded into the cellulose film and imparts anion permselectivity to allow binding and transport of hydrophobic anions. The number of binding sites is controlled by the amount of PDDAC present in the film. The electrochemical properties of the cellulose films are investigated first for the Fe(CN)₆^3-/4- model redox system and then for the accumulation and detection of triclosan (2,4,4‘-trichloro-2‘-hydroxydiphenyl ether, a hydrophobic polychlorinated phenol). Pure nanocellulose thin films essentially block the access to the electrode surface for anions such as Fe(CN)63- and Fe(CN)64-. In contrast, in the presence of cellulose−PDDAC films, accumulation and transport of both Fe(CN)63- and Fe(CN)64- in electrostatic binding sites occurs (Langmuirian binding constants for both are about 1.2 × 104 mol-1 dm3 in aqueous 0.1 M KCl). Facile reduction/oxidation at the electrode surface is observed. Triclosan, a widely used antifungal and antibacterial polychlorinated phenol is similarly accumulated into cationic binding sites (Langmuirian binding constant about 2.1 × 104 mol-1 dm3 in aqueous 0.1 M phosphate buffer pH 9.5) and is shown to give well-defined oxidation responses at glassy carbon electrodes. With a cellulose−PDDAC film electrode (80 wt % cellulose and 20 wt % PDDAC), the analytical range for triclosan in aqueous phosphate buffer at pH 9.5 is about 10^-6−10^-3 mol dm^-3.