Determination of urea with optical biosensor

Transparent triacetylcellulose membranes with immobilized pH indicator (neutral red) as well as with simultaneously immobilized urease and neutral red were used as optical sensors for determination of urea concentrations. Decomposition of urea with the enzyme urease is accompanied by evolution of ammonia. This changes the neutral red absorption, which is proportional to the substrate (urea) within certain concentration limits. As a result of the investigation, standard curve were plotted for determination of urea over the range of 1 to 500 mM using immobilized indicator and free urease. Simultaneous immobilization of indicator and urease permitted determination of urea in the interval 50 to 500 mM The membrane used contained 0.169 U urease activity on an area of 1.7 cm(2). The standard curves were in both cases plotted for 5min treatment of the substrate using the linear region of the kinetic curves for the corresponding substrate concentrations. A possible scheme of the interaction between the activated triacetylcellulose membrane and the indicator is proposed. The membranes obtained are suitable for repeated clinical and ecological applications where urea is to be determined.