We proposed a new method for counting the number of active bacteria by using microdroplet as an incubator (Fig. 1a). During the cultivation, the change of bacterium’s behavior or the change of chemical and physical property might be enhanced due to its small droplet volume. Therefore, by counting the number of droplet which indicates these changes, it might be possible to perform rapid viability assessment.
We have fabricated a microchannel chip to generate and store microdroplets (Fig. 1b), each of which contains single bacterium (E. coli K-12) at most. After formation of microdroplets, two inlets and outlet were sealed, and chip was placed into temperature-stabilized water bath to maintain optimal cultivation conditions.
Several microdroplets containing single E.coli were examined by optical microscopy and then the cultivation process was recorded at intervals of 30 minutes for 6 hours. The temperature of the water bath was varied and the cultivation process was screened for optimal growth conditions. The highest cultivation speed was observed for temperature of 37℃. By counting the number of active and dead bacteria in the colony inside the droplet it was possible to estimate the number of initially active E. coli.