The LOD values of the competitive immunoassays based on 7A3 for MN1-MN7 gradually decreased from 0.2 to 0.001 nM as the epitope distance of model analytes increased from 2.4 to 13.9 Å, and increased LOD values were observed for the longest model analytes, MN8 and MN9, with epitope distances of 16.4 and 19.0 Å, respectively (Fig. and Table ). Similarly, the LOD values of the competitive immunoassays based on 17B3 gradually increased and then decreased for MN1-MN9 with epitope distances of 2.4-19.6 Å (Fig. and Table ).