A QCM immunosensor to rapidly detect ractopamine using bio-polymer conjugate and magnetic β-cyclodextrins

An enzyme-amplified magnetic immunosensor was developed for the sensitive and selective detection of ractopamine (RAC) in fodder using a quartz crystal microbalance (QCM). Magnetic capture probes were prepared by immobilizing β-cyclodextrins (β-CD) on Fe 3 O 4 nanoparticles in order to enrich RAC. PowerVision (PV), a kind of enzyme–polymer complex with a high enzyme-to-antibody ratio, served as a signal label. Horseradish peroxidase (HRP) on the immnunocomplex, which arises from sandwich-type immunoreactions, causes 3,3′,5,5′-tetramethylbenzidine (TMB) to produce large amounts of sedimentation with a mass proportional to RAC. The large amounts of HRP on the PV greatly amplify the QCM sensor's signal. Under optimum conditions, the differences of the QCM frequency (Δ f ) are proportional to the concentration of RAC over the range from 0.03 to 25   ng   mL −1 . The limit of detection was 0.01   ng   mL −1 . More importantly, this assay's results in swine fodder samples were consistent with those of ELISA, with recoveries between 92.3% and 110%. Due to its high sensitivity, portability and selectivity, the immunosensor achieved reliable quantification of RAC in real fodder samples and has the potential to become an on-site screening tool to enhance food safety.