Fig. 5

Step-changes in the threshold point in response to ligand-binding. In two further experiments in R2, the threshold behaviour of dye-labelled M13 was monitored as a function of time and the addition of cp-mAb or a non-binding antibody. For each experiment, the data were fit globally using equation (26) with parameters χ₀ and χ₁ shared between each set of threshold measurements. For further experiment 2, 20 pmol mL⁻¹ V2 contained no antibody (blue), before 4.5 pmol mL⁻¹ cp-mAb was added (green). For further experiment 1, 23 pmol mL⁻¹ V2 initially contained no antibody (blue), 91 fmol mL⁻¹ mouse IgG2a isotype control was added (black) and then cp-mAb was added in two steps so that the concentration of cp-mAb was initially 91 fmol mL⁻¹ (purple) and then increased to 1.9 pmol mL⁻¹ (green). See Methods for more details. The threshold points derived from the fitted models have been plotted against time for, a further experiment 2 and for, b further experiment 1. Measurements have been represented by an arrow if the fitting implied that the sample could no longer sustain lasing. The error bars represent standard errors and the error bars that extend beyond the upper limit of the y-axis extend to infinity. See Supplementary Fig. 10 for an expanded version of this figure with the intensity against pump energy data for different points in the time series. Source data are provided as a Source Data file