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A copolymer with balanced hydrophilicity and hydrophobicity was synthesized by grafting butyl acrylate onto poly(vinyl alcohol) (PVA-g-BA). Films made from it had good urea permeability. After immobilization of the enzyme urease on the surface of it, the film was attached to the tip of an ammonia gas electrode to form an enzyme sensor. The sensor was able to detect urea in solution in the range of 6 to 600 mg/dL with a response time of about 5 min. It might be reused for over 100 times, and the reproducibility was very good. Therefore, it is very promising that this sensor may be commercialized for clinical use. The synthesis of PVA-g-BA was initiated with cerium ammonium nitrate, and the immobilization of urease was done by crosslinking with cyanuric chloride of glutaraldehyde. The former agent was proved to be more effective than the later. The amount of enzyme immobilized with the former were 26 and 13 times more than the one- and two-step methods with the latter, respectively.
Hsiue et al. (Wed,) studied this question.