A comparative study of immobilization techniques for urease on glass-pH-electrode and its application in urea detection in blood serum

Different techniques have been used (physical adsorption, physically entrapped sandwich and microencapsulation) for the immobilization of urease enzyme in tetramethylorthosilicate (TMOS) derived sol–gel matrix on the sensing surface of glass-pH-electrode. No significant leaching of enzyme occurs from the microencapsulated and physically entrapped enzyme sandwich films. Potentiometric techniques have been used for the estimation of urea concentration in each instance. Various parameters of biosensor performance have been studied which indicates that microencapsulation technique is a better method of enzyme immobilization in sol–gel films derived from TMOS. The advantage of microencapsulated biosensor over others include higher sensitivity (dpH/dp(C) = 2.4), lower detection limit of 52 μg mL −1, larger linear range (0.01–30 mM) of urea determination and reasonably long-term stability of about 25 days with 80% response signal.