A novel thermometric biosensor for fast surveillance of β-lactamase activity in milk

Regulatory restrictions on antibiotic residues in dairy products have resulted in the illegal addition of beta-lactamase to lower antibiotic levels in milk in China. Here we demonstrate a fast, sensitive and convenient method based on enzyme thermistor (ET) for the surveillance of beta-lactamase in milk. A fixed amount of penicillin G, which is a specific substrate of beta-lactamase, was incubated with the milk sample, and an aliquot of the mixture was directly injected into the ET system to give a temperature change corresponding to the remained penicillin G. The amount of beta-lactamase present in sample was deduced by the penicillin G consumed during incubation. This method was successfully applied to quantify beta-lactamase in milk with the linear range of 1.1-20 U mL(-1) and the detection limit of 1.1 U mL(-1). The recoveries ranged from 93% to 105%, with relative standard deviations (RSDs) below 8%. The stability of the column equipped in ET was also studied, and only 5% decrease of activity was observed after 60 days of use. Compared with the conventional culture-based assay, the advantages of high throughput, timesaving and accurate quantification have made this method an ideal alternative for routine use. (C) 2013 Elsevier B.V. All rights reserved.