Microtiter plates were coated with purified mAb (capture antibody, 4 μg/mL, 100 μL/well) in coating buffer and incubated at 4°C overnight. The plates were subsequently washed and blocked with 150 μL of blocking buffer. Then, 100 μL of the model analyte (10 μΜ) was added and incubated at 37°C for 1 h, followed by another washing procedure. Next, 100 μL of diluted HRP-labeled mAb (detecting antibody, 0.2 μg/mL) was added to each well, which was incubated for 1 h at 37°C. The TMB substrate solution was added after washing, 2 M H2SO4 was added to stop the reaction, and the OD values were measured at 450 nm. The measured OD values were used to represent the formation efficiency of the sandwich immunoassay by different mAb pairs. Specifically, an OD value below 0.1 was considered to be indistinguishable from the background, i.e., a signal to noise (S/N) ratio below 2.1, indicating that sandwich immunoassay establishment had failed, while OD values of 0.5-1.0 and above 1.0 represented medium and high formation efficiencies of sandwich immunoassays, respectively.