Analysis of β-lactam antibiotics using a microbial receptor protein-based biosensor assay

An optical biosensor assay for detection of beta-lactam antibiotics in milk based on a microbial receptor protein was developed. The assay uses a general sensor surface previously described with a small organic molecule (H1) immobilized. A conjugate between a beta-lactam (cephalosporin C) and a monoclonal H1 antibody is injected across the sensor surface before injection of the sample mixed with receptor protein. Receptor inhibited by beta-lactam residues in the milk sample will not bind to the sensor surface and the reduction in response is inversely related to the beta-lactam concentration of the sample. The detection limit for a number of commonly used beta-lactams was below or near the respective maximum residue limit and the relative standard deviation (CV) for penicillin G in milk was 6-12% in the interval 2.0-12.5 mg kg(-1). For application in the field further optimization is needed to solve problems related to non-specific binding to the sensor surface.