Solid-phase fluorescence immunoassay for detection of antibiotic residues in milk

We describe a rapid, inhibition immunoassay for several antibiotics found as residues in milk. The fluorophore is the recently developed compound, Cy-5(TM), and the excitation source is a semiconductor-diode laser. The solid-phase is the borosilicate glass surface (SiO2) of a capillary tube that has been treated with a silanizing reagent. beta-Lactam antibiotics (penicillin-G, ampicillin, cloxacillin, amoxicillin, ceftiofur and cephapirin) at the parts per billion level can be detected in a total assay time of less than three minutes. These assays were optimized to provide the greatest sensitivity at or near the regulatory safe/tolerance levels for the appropriate antibiotics. The potential for the use of this system for other types of assays will also be discussed.