Since a hapten cannot be effectively recognized by the immune system to induce subsequent antibody response, it should be first conjugated to a carrier protein. Thus, the carboxyl groups of all haptens were conjugated to BSA as immunogens and OVA as coating antigens to screen antisera and produce mAbs. The preparation steps of these hapten-protein conjugates are described in the Supplementary Information. Since the hapten-carrier ratio could influence the level of antibody response of the host animals, it was carefully controlled in the range of 19.3-23.6 for MEL haptens-BSA and in the range of 9.0-13.2 for NIA haptens-BSA and successfully characterized by MALDI-TOF-MS (Supplementary Fig. and Supplementary Table ).