, We thank W. Keiderling, A. Gerke, and W. Schubert from the Workshop facility of the MPIds for technical support

T. Thorsen, R. W. Roberts, F. H. Arnold, and S. R. Quake, Dynamic pattern formation in a vesicle-generating microfluidic device, Phys. Rev. Lett, vol.86, pp.4163-4166, 2001.

T. M. Squires and S. R. Quake, Microfluidics: Fluid physics at the nanoliter scale, Rev. Mod. Phys, vol.77, pp.977-1026, 2005.
DOI : 10.1103/revmodphys.77.977

URL : https://authors.library.caltech.edu/1310/1/SQUrmp05.pdf

, See the series of papers in the, Lab on a Chip" supplement in Nature, vol.442, pp.367-418, 2006.

B. T. Kelly, J. Baret, V. Taly, and A. D. Griffiths, Miniaturizing chemistry and biology in microdroplets, Chem. Commun, pp.1773-1788, 2007.
DOI : 10.1002/chin.200734246

URL : https://hal.archives-ouvertes.fr/hal-02148777

R. Seemann, M. Brinkmann, T. Pfohl, and S. Herminghaus, Droplet-based microfluidics, Rep. Prog. Phys, vol.75, p.16601, 2012.

M. T. Guo, A. Rotem, J. A. Heyman, and D. A. Weitz, Droplet microfluidics for high-throughput biological assays, Lab Chip, vol.12, pp.2146-2155, 2012.
DOI : 10.1039/c2lc21147e

E. Brouzes, M. Medkova, N. Savenelli, D. Marran, M. Twardowski et al., Droplet microfluidic technology for single-cell high-throughput screening, Proc. Natl. Acad. Sci. U.S.A, vol.106, pp.14195-14200, 2009.
DOI : 10.1073/pnas.0903542106

URL : http://europepmc.org/articles/pmc2732882?pdf=render

J. Baret, O. J. Miller, V. Taly, M. Ryckelynck, A. El-harrak et al., Fluorescence-activated droplet sorting (FADS): Efficient microfluidic cell sorting based on enzymatic activity, Lab Chip, vol.9, pp.1850-1858, 2009.
URL : https://hal.archives-ouvertes.fr/hal-02148757

J. Baret, Y. Beck, I. Billas-massobrio, D. Moras, and A. D. Griffiths, Quantitative cell-based reporter gene assays using droplet-based microfluidics, Chem. Biol, vol.17, pp.528-536, 2010.
DOI : 10.1016/j.chembiol.2010.04.010

URL : https://hal.archives-ouvertes.fr/hal-02148764

T. Satoh, K. Kodama, S. Ichikawa, S. Sugiura, and T. Kanamori, Pressure-driven microfluidic device for droplet formation with minimized dead volume, J. Chem. Eng. Jpn, vol.47, pp.841-847, 2014.
DOI : 10.1252/jcej.14we103

B. E. Debs, R. Utharala, I. V. Balyasnikova, A. D. Griffiths, and C. A. Merten, Functional single-cell hybridoma screening using droplet-based microfluidics, Proc. Natl. Acad. Sci. U.S.A, vol.109, pp.11570-11575, 2012.

S. L. Sjostrom, Y. Bai, M. Huang, Z. Liu, J. Nielsen et al., High-throughput screening for industrial enzyme production hosts by droplet microfluidics, Lab Chip, vol.14, pp.806-813, 2014.

B. L. Wang, A. Ghaderi, H. Zhou, J. Agresti, D. A. Weitz et al., Microfluidic highthroughput culturing of single cells for selection based on extracellular metabolite production or consumption, Nat. Biotechnol, vol.32, pp.473-478, 2014.

H. N. Joensson, M. L. Samuels, E. R. Brouzes, M. Medkova, M. Uhl-en et al., Detection and analysis of low-abundance cell-surface biomarkers using enzymatic amplification in microfluidic droplets, Angew. Chem. Int. Ed, vol.48, pp.2518-2521, 2009.

R. Arayanarakool, L. Shui, S. W. Kengen, A. Van-den, J. C. Berg et al., Single-enzyme analysis in a dropletbased micro-and nanofluidic system, Lab Chip, vol.13, pp.1955-1962, 2013.

D. Pekin, Y. Skhiri, J. Baret, D. L. Corre, L. Mazutis et al., Quantitative and sensitive detection of rare mutations using droplet-based microfluidics, Lab Chip, vol.11, pp.2156-2166, 2011.
URL : https://hal.archives-ouvertes.fr/hal-02148770

J. Clausell-tormos, A. D. Griffiths, and C. A. Merten, An automated two-phase microfluidic system for kinetic analyses and the screening of compound libraries, Lab Chip, vol.10, pp.1302-1307, 2010.

O. J. Miller, A. E. Harrak, T. Mangeat, J. Baret, L. Frenz et al., High-resolution dose-response screening using droplet-based microfluidics, Proc. Natl. Acad. Sci. U.S.A, vol.109, pp.378-383, 2012.
DOI : 10.1073/pnas.1113324109

URL : https://hal.archives-ouvertes.fr/hal-02136487

Q. Zhong, S. Bhattacharya, S. Kotsopoulos, J. Olson, V. Taly et al., Multiplex digital PCR: Breaking the one target per color barrier of quantitative PCR, Lab Chip, vol.11, pp.2167-2174, 2011.

V. Taly, D. Pekin, L. Benhaim, S. K. Kotsopoulos, D. L. Corre et al., Multiplex picodroplet digital PCR to detect KRAS mutations in circulating DNA from the plasma of colorectal cancer patients, Clin. Chem, vol.59, pp.1722-1731, 2013.

L. B. Pinheiro, V. A. Coleman, C. M. Hindson, J. Herrmann, B. J. Hindson et al., Evaluation of a droplet digital polymerase chain reaction format for DNA copy number quantification, Anal. Chem, vol.84, pp.1003-1011, 2012.

A. Didelot, S. K. Kotsopoulos, A. Lupo, D. Pekin, X. Li et al., Multiplex picoliter-droplet digital PCR for quantitative assessment of DNA integrity in clinical samples, Clin. Chem, vol.59, pp.815-823, 2013.

J. J. Agresti, E. Antipov, A. R. Abate, K. Ahn, A. C. Rowat et al., Ultrahigh-throughput screening in drop-based microfluidics for directed evolution, Proc. Natl. Acad. Sci. U.S.A, vol.107, pp.4004-4009, 2010.
DOI : 10.1073/pnas.0910781107

URL : https://hal.archives-ouvertes.fr/hal-02136491

L. Mazutis, J. Gilbert, W. L. Ung, D. A. Weitz, A. D. Griffiths et al., Single-cell analysis and sorting using droplet-based microfluidics, Nat. Protoc, vol.8, pp.870-891, 2013.

W. D. Ristenpart, J. Wan, and H. A. Stone, Enzymatic reactions in microfluidic devices: Michaelis-Menten kinetics, Anal. Chem, vol.80, pp.3270-3276, 2008.
DOI : 10.1021/ac702469u

K. Ahn, J. Agresti, H. Chong, M. Marquez, and D. A. Weitz, Electrocoalescence of drops synchronized by sizedependent flow in microfluidic channels, Appl. Phys. Lett, vol.88, p.264105, 2006.

U. K. Shim, R. T. Ranasinghe, C. A. Smith, S. M. Ibrahim, F. Hollfelder et al., Ultrarapid generation of femtoliter microfluidic droplets for single-molecule-counting immunoassays, ACS Nano, vol.7, pp.5955-5964, 2013.

J. Lim, P. Gruner, M. Konrad, and J. Baret, Micro-optical lens array for fluorescence detection in droplet-based microfluidics, Lab Chip, vol.13, pp.1472-1475, 2013.
DOI : 10.1039/c3lc41329b

URL : https://hal.archives-ouvertes.fr/hal-02129796

A. R. Abate and D. A. Weitz, Syringe-vacuum microfluidics: A portable technique to create monodisperse emulsions, Biomicrofluidics, vol.5, p.14107, 2011.
DOI : 10.1063/1.3567093

URL : http://europepmc.org/articles/pmc3073010?pdf=render

W. Li, E. W. Young, M. Seo, Z. Nie, P. Garstecki et al., Simultaneous generation of droplets with different dimensions in parallel integrated microfluidic droplet generators, Soft Matter, vol.4, pp.258-262, 2008.

T. Nisisako and T. Torii, Microfluidic large-scale integration on a chip for mass production of monodisperse droplets and particles, Lab Chip, vol.8, pp.287-293, 2008.

T. Nisisako, T. Ando, and T. Hatsuzawa, High-volume production of single and compound emulsions in a microfluidic parallelization arrangement coupled with coaxial annular world-to-chip interfaces, Lab Chip, vol.12, pp.3426-3435, 2012.

M. K. Mulligan and J. P. Rothstein, Scale-up and control of droplet production in coupled microfluidic flow-focusing geometries, Microfluid. Nanofluid, vol.13, pp.65-73, 2012.

D. Conchouso, D. Castro, S. A. Khan, and I. G. Foulds, Three-dimensional parallelization of microfluidic droplet generators for a litre per hour volume production of single emulsions, Lab Chip, vol.14, pp.3011-3020, 2014.

D. Langbein, Springer Tracts in Modern Physics Series, vol.178, 2002.

M. Brinkmann, Benetzung lateral strukturierter Oberflaechen, 2002.

J. Baret and M. Brinkmann, Wettability control of droplet deposition and detachment, Phys. Rev. Lett, vol.96, p.146106, 2006.
DOI : 10.1103/physrevlett.96.146106

URL : https://hal.archives-ouvertes.fr/hal-02136454

M. J. Fuerstman, A. Lai, M. E. Thurlow, S. S. Shevkoplyas, H. A. Stone et al., The pressure drop along rectangular microchannels containing bubbles, Lab Chip, vol.7, pp.1479-1489, 2007.
DOI : 10.1039/b706549c

M. T. Sullivan and H. A. Stone, The role of feedback in microfluidic flow-focusing devices, Philos. Trans. A: Math. Phys. Eng. Sci, vol.366, pp.2131-2143, 2008.

Z. Huang, Kinetic fluorescence measurement of fluorescein di-beta-D-galactoside hydrolysis by beta-galactosidase: Intermediate channeling in stepwise catalysis by a free single enzyme, Biochemistry, vol.30, pp.8535-8540, 1991.

S. Sakakihara, S. Araki, R. Iino, and H. Noji, A single-molecule enzymatic assay in a directly accessible femtoliter droplet array, Lab Chip, vol.10, pp.3355-3362, 2010.
DOI : 10.1039/c0lc00062k

C. Holtze, A. C. Rowat, J. J. Agresti, J. B. Hutchison, F. E. Angile et al., Biocompatible surfactants for water-in-fluorocarbon emulsions, Lab Chip, vol.8, pp.1632-1639, 2008.
DOI : 10.1039/b806706f

T. Orazio, C. Guaragnella, M. Leo, and A. Distante, A new algorithm for ball recognition using circle Hough transform and neural classifier, Pattern Recognit, vol.37, pp.393-408, 2004.

H. Schreier, J. Orteu, and M. A. Sutton, Image Correlation for Shape, Motion and Deformation Measurements, 2009.
DOI : 10.1007/978-0-387-78747-3

URL : https://hal.archives-ouvertes.fr/hal-01729219

Y. Skhiri, P. Gruner, S. Semin, Q. Brosseau, D. Pekin et al., Dynamics of molecular transport by surfactants in emulsions, Soft Matter, vol.8, pp.10618-10627, 2012.
URL : https://hal.archives-ouvertes.fr/hal-02148774

, for more details about the methodology and the microfluidic platform