A simple and rapid competitive enzyme-linked immunosorbent assay (cELISA) for high-throughput measurement of secretory immunoglobulin A (sIgA) in saliva

A simple competitive enzyme-linked immunosorbent assay (cELISA) was established for rapid measurement of secretory immunoglobulin A (sIgA) in saliva. The method was based on competitive reaction between the immobilized IgA and free IgA in the solution for the limited amount of horseradish peroxidase-conjugated rabbit anti-human IgA. In comparison with the conventionally used Sandwich ELISA, the cELISA is simpler, low-cost, and shows better reproducibility since it is not affected by the variation of capture antibodies from different batches. The assay time was also significantly reduced from more than 5 h to less than 3 h. Different curve-fitting models were compared, among which the fully specified logit-log model gave the best results. The linear working range and limit of detection were found to be 0.1–100 μg mL−1 and 0.05 μg mL−1, respectively. Matrix effects of saliva samples were investigated and a reasonable range of dilution factors were proposed. The developed method offers a very practical approach for high-throughput measurement of sIgA in saliva samples.