An increased CPRG substrate concentration combined with a different detergent, Saponin, and an optimal wavelength recording markedly increased the sensitivity for the detection of β-galactosidase activity (≈4-fold increase). Moreover, the improved protocol resulted in increased linear time-dependent recording of enzymatic activity once cells had been lysed, and a more stable and reproducible assay to detect a ligand-stimulus with the reporter cells. The optimal time length of exposure to a stimulus was ligand-dependent.