Evaluation of a Gluconobacter oxydans whole cell biosensor for amperometric detection of xylose

Whole cells of Gluconobacter oxydans were employed in a microbial sensor for xylose determinations using Clark-type electrodes. Bacterial cells were immobilized on chromatographic paper by simple physical adsorption and attached to the surface of the electrodes. The lower limit of xylose detection was approximately 0·5 mM and measurements were useful up to at least 20 mM xylose. Physiological buffers showed little effect on biosensor function. Responses were highly reproducible, showing a standard deviation of 6·7% over 10 consecutive measurements. Whole cell biosensors were relatively stable, retaining 60% of initial activity after 35 days of dry storage at 4°C. Xylose detection was not significantly affected by the presence of xylitol, suggesting that biosensors will be useful in monitoring conversions of these compounds. However, glucose or ethanol elicited a 10-fold higher response than xylose at equal concentrations (1 mM). Such interfering materials will need to be controlled or concurrently monitored in specific sensor applications.