Magnetic Separation Immunosensor Based on Enzyme-linked Gold Nanocomposite Probe for Detection of Ractopamine

A magnetic separation competitive immunosensor based on novel enzyme-linked gold nanocomposite probes (E-GNPs) was constructed for detection of ractopamine ( RAC). Through the specific interaction between streptavidin and biotin, horseradish peroxidase ( HRP) was labeled on the antibody that was modified on the surface of gold nanoparticles (AuNPs) by electrostatic assembly method to obtain E-GNPs. Ovalbumin (OVA )-RAC hapten coated magnetic beads ( MBs ) was introduced for a competitive reaction, and quantitative analysis of the target was achieved by a color reaction. With the change of the concentration of target molecule RAC, the color of the enzyme-catalyzed substrate changed, and the concentration of RAC had a linear relationship with the color signal intensity. The UV-vis absorption spectroscopy characterization results showed that one E-GNP could carry 11 HRP molecules, which made the immunosensor highly sensitive. The prepared sensor was successfully used for detection of RAC with a detection limit of 1.75 pg/ mL, showing 10 times higher sensitivity than that of traditional ELISA method. Cross-reaction experiments showed that the sensor had good selectivity for RAC, and could be applied to real samples such as pork, beef and mutton, with spiked recoveries ranging from 88. 3% to 103. 4%. This analytical method provided a new idea for rapid screening of RAC in animal-derived foods.