Electrochemical properties of an osmium(II) copolymer film and its electrocatalytic ability towards the oxidation of ascorbic acid in acidic and neutral pH

Copolymerization of an osmium(II) functionalized pyrrole moiety, osmium-bis-NN'-(2,2'-bipyridyl)-N-(pyridine-4-ylmethyl-(8-pyrrole-1yl-octyl)-amine)chloride (1) with 3-methylthiophene was carried out. The resulting conducting polymer film exhibited a clear redox couple associated with the Os3+/2+ response and the familiar conducting polymer backbone signature. The effect of film thickness upon the redox properties of the copolymer was investigated in organic electrolyte solutions. Scanning electron micrographs (SEM) along with energy dispersive X-ray (EDX) spectra of the copolymerized films were undertaken, both after formation and redox cycling in neutral buffer solution. These clearly show that electrolyte is incorporated into the polymer film upon redox cycling through the Os3+/2+ redox system. The Os3+/2+ response associated with the copolymer was seen to be significantly altered in the presence of ascorbic acid both in acidic and neutral pH buffer solutions. This pointed to an electrocatalytic reaction between the ascorbic acid and the Os3+ form of the copolymer. Under acidic conditions the copolymer film exhibited a sensitivity of 1.76 (+/- 0.05) mu A/mM with a limit of detection (LOD) of 1.45 mu M for ascorbic acid. Under neutral pH conditions the copolymer exhibited a sensitivity of 19.26 (+/- 1.05) mu A/mM with a limit of detection (LOD) of 1.28 mu M for ascorbic acid.