Fig. 3.

MMP assay performance. (A) We test the detection limits of the assay using serial dilutions of known concentrations of collagenase. A linear correlation exists between droplet intensity and number of molecules reacted for greater than 700 molecules per droplet up to 300,000 molecules per droplet, indicating a large dynamic range for detection. These correlations can be used to estimate the time-averaged number of molecules secreted by single cells. (B) The signal becomes saturated for concentrations of greater than 300,000 molecules per droplet, and there is little time dependence of the signal beyond 3 h.