Ultrasensitive determination of ractopamine based on dual catalytic signal amplification by Pd nanocubes and HRP using a flow injection chemiluminescence immunoassay
A rapid and highly sensitive flow injection chemiluminescence immunoassay was developed to detect ractopamine residues in pork products. Palladium nanocubes with excellent catalytic performance for a traditional luminol–PIP–H2O2 chemiluminescence system were used as effective carriers to connect a ractopamine antibody and horseradish peroxidase (HRP). Double amplification of a chemiluminescence signal was realized because of palladium nanocubes and HRP. Carboxyl-modified resin beads were used as suitable materials to load ractopamine-coating antigens due to their good biocompatibility and large specific surface area. Based on the principle of competitive immunity, ractopamine standard solution would compete with antigen loaded on carboxyl resin beads for limited binding sites on a ractopamine antibody. Thus, the chemiluminescence intensity of an immunosensor has a linear negative correlation with the logarithm value of ractopamine concentration. Under optimal experimental conditions, the detection range of ractopamine was 0.005–1000 ng mL−1, and the limit of detection (LOD) was 1.7 pg mL−1 (S/N = 3). The proposed immunoassay possessed acceptable accuracy, high specificity and reproducibility and RAC was examined in pork and pig feed with satisfactory results, which would provide a better prospect for the detection of small molecules in food and environment analysis.