Precise analysis of the aquatic cells and their responses to the toxic chemicals, i.e., water disinfective agents, is of crucial importance due to their role in the ecosystem. We demonstrate the application of the droplets based millifluidic tool for isolating and longtime monitoring of single Paramecium tetraurelia cells using a large number of water-in-oil emulsion droplets. Due to the automated monitoring of the fluorescence signal, the droplets containing cells are distinguished from the empty reservoirs. A viability indicator is used to follow the metabolic dynamic of the cells in every single droplet. Finally, we perform ecotoxicity tests in droplets, exposing the encapsulated paramecia cells to silver nitrate for determination of EC50 levels, and compare the output with the conventional microtiter plate assay.

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See supplementary material at http://dx.doi.org/10.1063/1.4944869 for movies and additional figures. Supplementary materials contain several subchapters: 1. Detection of the optical signal. Enclosed Fig. 1S describes the principle for collection of the emission light, using virtual filtering. 2. Adjustment of cell density. 3. Determination of the droplets' filling factor. Enclosed Fig. 2S describes the fill rate of the droplet compared with theoretical values of the Poisson distribution for the cell densities. 4. Ecotoxicity assays. Enclosed Fig. 3S shows the fluorescence signal of droplets with different concentrations of AgNO3. Supplementary video S1 demonstrates the single paramecia encapsulated inside a droplet. Supplementary video S2 corresponds to the case, when two paramecia cells filling the droplet. Finally, supplementary video S3 shows the division events of single paramecia cells, encapsulated inside the droplet.

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