Amperometric enzyme electrode for theophylline

Abstract

An amperometric biosensor for theophylline, based on the recently isolated enzyme theophylline oxidase, is described. The enzyme is entrapped, together with a ferricytochrome C cofactor, within a polymeric (Nafion) coating. The anodic detection (at +0.4 V versus Ag–AgCl) is facilitated by the addition of a redox-mediating hexacyanoferrate(III) ion. The influence of various experimental variables is described. The limit of detection is 2 × 10^–6 mol dm^–3 theophylline, with linearity prevailing up to 3 × 10^–4 mol dm^–3. The fast response and wash times permit rapid flow-injection measurements, with a frequency of 180 samples h^–1 and a relative standard deviation of 3.0–4.0%. Prospects of using this electrode for clinical diagnostics are discussed.