Electropolymerised Phenolic Films as Internal Barriers for Oxidase Enzyme Biosensors

The properties of electropolymerised phenolic films at amperometric needle electrodes were investigated and their applicability as selective, internal barriers for potential in vivo oxidase enzyme based biosensors evaluated. Polyphenol, poly(phenol red) and dual layer poly(phenol red)/poly(4-aminophenol) films were formed by electropolymerisation and compared with a solvent deposited sulfonated polyether ether sulfone-polyether sulfone (SPEES-PES) membrane. Phenol red had two distinct cyclic voltammetry peaks on platinum: an oxidative peak at +0.70 V and a reduction peak at -0.2 V vs. Ag/AgCl, respectively. Also, the film enhanced the oxidation of hydrogen peroxide by a factor of 3-4, making it an attractive barrier for oxidase based biosensors. Lactate sensors made with polyphenolic electropolymers and solvent deposited SPEES/PES were compared for selectivity and lactate response; the latter showed better selectivity against acetaminophen but less selectivity against ascorbic acid. When sensors were sterilised by standard gamma irradiation for in vivo application, the polyphenolic films degraded and lost selectivity, whilst SPEES/PES survived unchanged. Salivary lactate was monitored during exercise with electropolymerised film sensors and demonstrated mean lactate increases of 0.3-0.6 mM.