Four Hapten Spacer Sites Modulating Class Specificity: Nondirectional Multianalyte Immunoassay for 31 β-Agonists and Analogues

Immunoassay methods are important for monitoring beta-agonists illegally used for reducing animal fat deposition in livestock. However, there is no simultaneous screening surveillance immunoassay for detecting various beta-agonist chemicals that are possibly present in food. In this study, through the use of an R-(-)-salbutamol derivative as the immunizing hapten, an antibody recognizing 31 beta-agonists and analogues was generated for the first time. Three-dimensional quantitative structure-activity relationship (3D QSAR) revealed that strong steric and hydrophobic fields around the hapten spacer near C-2, as well as a chirality at C-1', dominantly modulated the class specificity of the raised antibody. However, a hapten spacer linked at C-2' or C-1 would lead to a narrow specificity, and the spacer charge at C-6 could affect the raised antibody specificity spectrum. A class specificity competitive indirect enzyme-linked immunosorbent assay (ciELISA) was established with an ideal recovery ranging from 81.8 to 118.3% based on the obtained antibody. With a good agreement to the HPLC/MS method, the proposed ciELISA was confirmed to be reliable for the rapid surveillance screening assay of beta-agonists in urine. This investigation will contribute to the rational design and control of the immunoassay specificity.