Application of experimental design techniques to optimize a competitive ELISA

This paper describes the application of experimental design techniques to optimize a sensitive ELISA for a hapten molecule with a calibration range of 0-1000 pg/ml. Ten factors that were expected to affect the assay performance were initially screened, followed by factorial experiments to delineate the effects of the critical factors identified at the screening stage. Assay performance was evaluated using a unique rating system based on standard curve reproducibility, assay detection limits and the use of desirability functions. This rating system allowed multiple responses to be evaluated simultaneously. It was found that the substrate incubation time and enzyme label lot played an important role, while dilutions of the enzyme label and the anti-hapten antibody showed significant interaction. These observations were in good agreement with optimal assay conditions based on historical data collected over a period of two to three years. Application of experimental design techniques enabled us to confirm the significance of the factors affecting the assay within a three month period, with a minimum number of experiments. In addition, information on interaction between factors were determined.