Real-time growth record of bacteria in microbe observation and cultivation array (MOCA). (a,c) Growth curves of (a) Escherichia coli and (c) Bacillus subtilis with different initial cell concentrations (the lower the transmission, the larger the cell population). Each curve represents the growth in an individual droplet. (b,d) Threshold growth time distribution versus (b) E. coli and (d) B. subtilis cell concentrations. The threshold growth time was defined as the time when the normalized transmission intensity of a droplet intersected 0.99 (Figure 3a and3c, red dotted line).