부산대학교 도서관

A simple, reliable, low cost, and portable biosensor has been developed for direct measurement of urea levels in serum samples. It is based on hydrolysis of urea by immobilized urease, generating ammonia that is estimated by modified Berthelot method using simple optical detection system. The immobilization of urease was achieved in agarose guar-gum composite film for the first time which offered an excellent retention of enzyme activity (90%–95%) with negligible leaching and good operational stability. The optical detection system involving LED light, optical fiber, and phototransistor provides simple and portable measurement system. The sensor shows linear response in the wide range of urea concentration from 0.025 to 10 mM with reusability for 10 cycles and superior storage stability of 180 days. The fabricated biosensor was successfully employed for measurement of normal and abnormal urea levels in serum samples with accuracy of 96% using very small sample volume ( $15~\mu \text{l}$ ). It showed an excellent correlation ( $r^{2}=0.99$ ) for determination of urea levels with that of using Siemens autoanalyzer.