Figure 7

Responses of urease biosensor to 6 mM urea (a) and calibration curves (b) for single- and two-layer membranes. Single-layer urease membranes: 1 - with no zeolite; 2 - with a mixture of 5% zeolite and 5% urease. Two-layer membranes, which included: 3 - 5% urease in the first layer and 5% zeolite in the second layer; 4 - 5% zeolite in the first layer and 5% urease in the second layer; 5 - 5% zeolite in the first layer, a mixture of 5% zeolite and 5% urease in the second layer; 6 - 10% zeolite in the first layer, a mixture of 10% zeolite and 5% urease in the second layer; and 7 - a mixture of 5% urease and 5% zeolite in the first layer, a mixture of 5% urease and 5% zeolite in the second layer. Measurements were conducted in 5 mM phosphate buffer, pH 7.2.