Abstract
A new optical urea biosensor based on urease (Urs) physically attached to a pH optode made from Nile Blue (NB) chromoionophore-doped kappa-carrageenan (KC) membrane is described in this paper. The immobilized Urs on the biosensor surface catalyzed the hydrolytic decomposition of urea into ammonium hydroxide, a pH changed to a more basic condition, and resulted in a colour change of the pH sensor membrane from blue to violet, which can be quantified reflectometrically using a fibre optic reflectance spectrophotometer. A linear relationship was perceived between the reflectance intensity of the KC membrane-based biosensor and the urea concentration in the range of 0.001–100mM with the detection limit calculated at 0.001mM. The response time of the urea biosensor was 10min, and no significant discrepancy was noted for the results obtained from the direct analysis of urine samples by both the reflectance catalytic biosensor and the UV–vis spectrophotometric standard method based on the p-dimethylaminobenzaldehyde (DMAB) reagent.
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