Immunochemical assays for direct sulfonamide antibiotic detection in milk and hair samples using antibody derivatized magnetic nanoparticles

Two direct enzyme-linked immunosorbent assays (ELISAs) have been developed for detection of sulfonamide antibiotic residues in milk samples. One of them is using magnetic nanoparticles (MNP) for target capture/enrichment (Ab-MNP-ELISA), and the second is performed using microtiter plates. Selective polyclonal antibodies, raised against 5-6-(4-amino-benzenesulfonylamino)-pyridin-3-yl]-2-methyl-pentanoic acid (SA1), used in combination with an enzyme tracer prepared with the same hapten, has allowed us to reach a limit of detection (LOD) lower than 0.5 microg L(-1) for both ELISA formats. Sulfapyridine, sulfamethoxypyridazine, sulfathiazole, and sulfachloropyridazine are detected below the maximum residue limits established by the European Union for these antibiotics in milk (100 microg L(-1)). Matrix effects and accuracy studies performed with full-cream milk and hair extracts indicated a lack of interference from these sample matrices and very good recovery values, especially when using the Ab-MNP format. Milk samples and hair extracts can be measured without any previous treatment. The results demonstrate the high potential of these methods as screening tools for food safety and inspection controls.