Integrated disposable electrochemical immunosensors for the simultaneous determination of sulfonamide and tetracycline antibiotics residues in milk.

The design, preparation and analytical performance of a novel integrated amperometric immunosensor based on the immobilization of selective capture antibodies on the surface of Protein G-modified screen-printed dual carbon electrodes (SPdCEs) for the multiplexed determination of sulfonamide and tetracycline antibiotics residues in milk is reported in this work. Protein G was covalently immobilized onto a 4-aminobenzoic acid (4-ABA) film grafted on the disposable electrode, and a direct competitive immunoassay using horseradish peroxidase (HRP)-labeled tracers was performed. The amperometric responses measured at -0.2 V vs. the silver pseudo-reference electrode of the SPdCE upon the addition of H2O2 in the presence of hydroquinone (HQ) as mediator were used to monitor the extent of the immunoreactions. The developed methodology showed very low limits of detection (in the low ppb level) for sulfonamide and tetracycline antibiotics tested in untreated milk samples, and a good selectivity against other antibiotic residues frequently detected in milk and dairy products. The usefulness of the dual immunosensor was demonstrated by analyzing spiked milk samples as well as a reference milk containing a certified oxytetracycline (OTC) content. Good recoveries were attained in an analysis time of 30 min.