Enzyme-antibody dual labeled gold nanoparticles probe for ultrasensitive detection of κ-casein in bovine milk samples

A dual labeled probe was synthesized by coating gold nanoparticles (AuNPs) with anti-κ-CN monoclonal antibody (McAb) and horseradish peroxidase (HRP) enzyme on their surface. The McAb was used as detector and HRP was used as label for signal amplification catalytically oxidize the substrate. AuNPs were used as bridges between the McAb and HRP. Based on the probe, an immunoassay was developed for ultrasensitive detection of κ-CN in bovine milk samples. The assay has a linear response range within 4.2-560 ng mL−1. The limit of detection (LOD) was 4.2 ng mL−1 which was 10 times lower than that of traditional McAb-HRP based ELISA. The recoveries of κ-CN from three brand bovine milk samples were from 95.8% to 111.0% that had a good correlation (R2=0.998) with those obtained by official standard Kjeldahl method. For higher sensitivity and as simple as the traditional ELISA, the developed immunoassay could provide an alternative approach for ultrasensitive detection of κ-CN in bovine milk sample.