Polymer films as permselective coatings for H2O2-sensing electrodes

The performance of amperometric biosensors based on oxidation of the H2O2 generated by an oxidase suffers frequently from interference due to electrooxidizable species in a sample. For example, an effective biosensor of this type for the neurotransmitter, glutamate, in brain extracellular fluid (ECF) should show little or no amperometric response to readily oxidizable dopamine (DA) and ascorbate (AA), which are common constituents of ECF. In this work, platinum electrodes treated with four different polymeric, permselective films are compared quantitatively in terms of sensitivity to H2O2, DA and AA; and selectivity for H2O2 relative to either interferent. Here, the selectivity is defined as the ratio of the H2O2 sensitivity to the interferent sensitivity. Platinum electrodes coated with electrodeposited, overoxidized polypyrrole (OPP) and polyphenylenediamine films display H2O2 selectivities relative to AA of ⩾130 and ⩾240, respectively, and relative to DA of ⩾100 and 80, respectively. The impressive rejection of DA by OPP films observed in this study contrasts with published results showing enhanced DA permeability of polypyrrole electrode coatings. Nafion- and polyaniline-coated electrodes give inferior selectivity performance. The OPP-treated electrodes are judged superior overall given the best combination of H2O2 sensitivity (390 nA μM−1 cm−2), detection limit (0.5 μM), response time (∼5 s), and stability (>2 weeks), in addition to high H2O2 selectivities.