Abstract: An optical biosensor for urea measurements was developed. The operation of the sensor is based on the well-known urease enzyme-catalyzed hydrolysis of urea. The ammonium ions liberated in the reaction are detected with an ion selective optode membrane containing nonactin as ion selective ionophore and ETH 5294 chromoionophore in a thin (1 µm) plasticized poly(vinylchloride) film. The basic sensing element was home made of a microscope glass slide, a HeNe laser light source, photodiode light detector and light in coupling, de-coupling elements. The transducer membrane and the enzyme containing reaction layer were sandwich-cast with spin coating onto the surface of the sensing slide. The attenuation of the laser light propagating inside the glass wave-guide was used as signal for urea measurements. With this arrangement membranes provided good sensitivity (0.05 absorption unit when going from 0.1 to 1 mM urea) and short (16-20 s) response time. Taking advantage on the improved response time, flow injection urea measurements were made in the 0.01-2 mM concentration range. Thirty sample/hour analysis-rate, good peak-to-peak reproducibility (RSD=0.02) and recovery (95-104%) was achieved with buffer diluted urea solutions. Applications for the analysis of real samples are planned to do in the future.

Abstract: An all-solid-state anionic surfactant electrode type was developed using teflonized graphite rods coated with electrochemically prepared polypyrrole film as electric connector support. The measuring membrane of the electrodes was made of ion-pairs formed with the appropriate anionic and cationic surfactants incorporated into plasticized poly(vinylchloride) film. Preparation procedure for the ion-pair is described briefly in the text. The electrochemical properties of the electrode were studied and the function of the electrode was tested. Due to the well defined charge transfer mechanisms at the graphite-polypyrrole-membrane interfaces the surfactant electrode showed good stability. The lower limit of detection was in the range of 0.5-1 muM in case of the different surfactants tested. Due to the relatively fast response time and the good stability of the electrode, a sample rate of 30 sample/h in flow injection determinations could be achieved.