Fluorescent immunoassay for determination of penicillin and sulphonamide residues in milk using carboxylic magnetic nanoparticles

A fluorescent immunoassay for separate and simultaneous determination of penicillin (PEN) and sulphadimethoxine (SDM) in milk was developed. Monoclonal antibodies immobilised on carboxylic magnetic nanoparticles (MNPs) were used. It was proved that the protein A-oriented immobilisation method (OI) provided a 1.5-times more sensitive assay than the random immobilisation one (RI). The activation of MNPs with a mixture of N-(3-dimethylaminopropyl)-N-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) ensured a five-times higher sensitivity of immunoassay than the activation using EDC. The linearity of standard curves in milk was: 3/10ng/mL PEN (OI and RI), 50/250ng/mL SDM (OI), and 50/500ng/mL SDM (RI).