Immunosensor based on magnetic relaxation switch and biotin-streptavidin system for the detection of Kanamycin in milk

A rapid, sensitive, and simple immunosensor was developed for the detection of Kanamycin (KM) in milk. This immunosensor is based on magnetic relaxation switch (MRS) assay and biotin-streptavidin system (B-SA system). The target analyte (KM) competed with those on the surface of the superparamagnetic iron oxide (SPIO) nanoparticles and hence affected the formation of SPIO aggregates. The dispersed and aggregated states of SPIO can modulate the spin-spin relaxation time (T(2)) of the neighboring water molecule. T(2) was then changed as an effect of the target analyte. The B-SA system was used to amplify the SPIO binding, thus enhance the sensitivity. The detection working was 1.5 to 25.2ngmL(-1) and limit of detection (LOD) was determined to be 0.1ngmL(-1). The LOD of the immunosensor decreased tenfold, and its analysis time (45min) was much shorter than that of enzyme-linked immunosorbent assay (6h to 8h). The average recoveries of the KM at various spiking levels ranged from 80.2% to 85.6% with a relative standard deviation (RSD) below 4.0%. The results showed that the MRS immunosensor was a promising platform for the determination of small molecular residues because of its high sensitivity, specificity, homogeneity, and speed.