Screening of penicillin residues in milk by a surface plasmon resonance-based biosensor assay: comparison of chemical and enzymatic sample pre-treatment

A biosensor-based immunoassay for the screening of penicillin residues in milk was developed. The BIAcore biosensor which was employed was based on surface plasmon resonance detection. One commercial antibody against ampicillin which had much higher affinity for open beta-lactam ring than for closed ring was chosen. Two different pre-treatments were tested prior to the biosensor assay to open the ring in order to increase the assay sensitivity. These two ways were enzymatic (penicillinase) and chemical pre-treatment of the samples. Limits of detection for ampicillin in milk were 33 and 12.5 μg l −1 after enzymatic and chemical pre-treatment, respectively. There were no cross-reactions with cephalosporins and other families of antibiotics or proteins in the buffer and in milk after both the pre-treatments. Percentages of cross-reactivity with nine tested penicillins were often clearly higher in milk than in buffer. Moreover, a lack of sensitivity after penicillinase pre-treatment was observed. Conversely, penicillins G and penicillins M could be detected at or below their respective MRLs (4 and 30 μg l −1 in milk) and ampicillin and amoxicillin could be detected only at about three MRLs after chemical pre-treatment. However, the enzymatic pre-treatment was much easier to perform and led to more stable results.