A preliminary study of a biosensor based on flow injection of the recognition element

A biosensor based on flow injection of the recognition element has been developed. As a model a pH-transducer was used, and urease was chosen as the recognition element. The pH-transducer was immersed in an internal flow-through chamber which was in contact with the sample solution via a semi-permeable membrane. The recognition element, urease, was injected into the buffer solution passing through the biosensor. The enzyme catalysed the hydrolysis of urea and the concomitant increase in pH was recorded. The biosensor response time was about three minutes at a constant flow rate of 0.05 ml/min. The linear range of the calibration curve of the biosensor was 0 - 5 mM. The observed detection limit was approximately 0.1 mM. The sample throughput was 6 - 12 per hour. The pH-response of the biosensor, for a sample solution containing urea (3.26 mM), showed a reproducibility (r.s.d) of 28% (n = 5) and a repeatability (r.s.d.) of 8% (n = 5). Operation at elevated temperatures (up to 50 degrees C) was demonstrated. The presence of glucose (28 mM), acetone (6.7 mM), citric acid (0.2 mM) or sodium acetate (0.6 mM) in the sample solution did not interfere with the sensor response. A lowering of the biosensor response which was observed in the presence of copper ions (due to urease inhibition) could be completely eliminated by adding EDTA to the urease solution. Thus, this work demonstrates a new type of biosensors, based on SIRE-technology (Sensors with Injectable Recognition Elements), which show high accuracy and stability, quick response and high sample throughput. These features suggest the suitability of the system for automation. Such sensors should readily be combined with other enzymes or enzyme systems. The enzyme (urease) cost per analysis (injection) for the biosensor was estimated to be approximately US$0.02. This could be substantially reduced by further optimisation and miniaturisation. (C) 1996 Elsevier Science Limited