Penicillinase was immobilized by glutaraldehyde-bovine serum albumin and sodium alginate was used for the construction of enzyme biosensors in determination of trace penicillin in milk. Penicillinase activity was determined by potentionmetric method. At low concentrations, the response time of the electrode modified by the method of crossing-link was 30～60 s, and the electrode showed high sensitivity. Linear detection range from 1.40×10 -3 to 3.36×10 -2 mmol/L in PBS and from 5.61×10 -2 to 3.36× 10 -1 mmol/L in milk were achieved. The electrode can be used for at least 7 d with perfect reproducibility during the first 4 d. The life of the electrode was 30 d.
