Selectivity enhancement of an immobilized apple powder enzymatic sensor for dopamine

An enzymatic dopamine sensor was prepared by covering the gas membrane of a dissolved oxygen probe with a polycarbonate membrane in which pretreated apple fines were immobilized, followed by another polycarbonate membrane precoated with a Nafion film on the outside. The cationic exchange property of the Nafion film and its preclusion of the anionic interferents from entering the biofilm resulted in significant enhancement of the sensor selectivity and the linear calibration range for dopamine. However, the additional diffusion resistance introduced by the Nafion film diminished the sensor response or sensitivity and increased the response and baseline recovery times for a given dopamine concentration. Nevertheless, the exclusion of the various interferents and the reduced concentration of the solutes in the biofilm reduced contamination and deactivation of the enzymes, resulting in better sensor stability, reproducibility and service life.