Mass Activated Droplet Sorting (MADS) Enables High-Throughput Screening of Enzymatic Reactions at Nanoliter Scale

Angew Chem Int Ed Engl. 2020 Mar 9;59(11):4470-4477. doi: 10.1002/anie.201913203. Epub 2020 Jan 28.


Microfluidic droplet sorting enables the high-throughput screening and selection of water-in-oil microreactors at speeds and volumes unparalleled by traditional well-plate approaches. Most such systems sort using fluorescent reporters on modified substrates or reactions that are rarely industrially relevant. We describe a microfluidic system for high-throughput sorting of nanoliter droplets based on direct detection using electrospray ionization mass spectrometry (ESI-MS). Droplets are split, one portion is analyzed by ESI-MS, and the second portion is sorted based on the MS result. Throughput of 0.7 samples s-1 is achieved with 98 % accuracy using a self-correcting and adaptive sorting algorithm. We use the system to screen ≈15 000 samples in 6 h and demonstrate its utility by sorting 25 nL droplets containing transaminase expressed in vitro. Label-free ESI-MS droplet screening expands the toolbox for droplet detection and recovery, improving the applicability of droplet sorting to protein engineering, drug discovery, and diagnostic workflows.

Keywords: biocatalysis; droplet microfluidics; high-throughput screening; mass spectrometry; microreactors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algorithms
  • Amines / analysis*
  • Enzyme Activation
  • Enzyme Assays / methods*
  • Feasibility Studies
  • High-Throughput Screening Assays / methods*
  • Imidazoles / chemistry
  • Microfluidic Analytical Techniques
  • Microfluidics / methods*
  • Pyridines / analysis*
  • Pyridines / chemistry
  • Spectrometry, Mass, Electrospray Ionization
  • Transaminases / metabolism*


  • Amines
  • Imidazoles
  • Pyridines
  • Transaminases