Sensitive detection of small molecules by competitive immunomagnetic-proximity ligation assay

A novel detection method of small molecules, competitive immunomagnetic-proximity ligation assay (CIPLA), was developed and described in this report. Through the proximity effect caused by special proximity probes we prepared, small molecules can be detected using only one monoclonal antibody. CIPLA overcomes the obstacle that the proximity ligation assay (PLA) cannot be used in small molecular detection, as two antibodies are unable to combine to one small molecule due to its small molecular structure. Two small molecular compounds, clenbuterol (CLE) and ractopamine (RAC), were selected as targets for CIPLA. The limit of detection (LOD) reached 0.01 ng mL(-1), which was 10-50-fold lower than ELISA. With 5 orders of magnitude of the dynamic range achieved, the excellent sensitivity and broad dynamic range of CIPLA are noted. It can be applied widely in the sensitive detection of many other small molecular materials such as pesticides, additives in food, drugs, and biological samples, which have great significance in both theoretical and practical aspects.