Accurate dispensing of volatile reagents on demand for chemical reactions in EWOD chips

Lab Chip. 2012 Sep 21;12(18):3331-40. doi: 10.1039/c2lc40244k. Epub 2012 Jul 23.


Digital microfluidic chips provide a new platform for manipulating chemicals for multi-step chemical synthesis or assays at the microscale. The organic solvents and reagents needed for these applications are often volatile, sensitive to contamination, and wetting, i.e. have contact angles of <90° even on the highly hydrophobic surfaces (e.g., Teflon® or Cytop®) typically used on digital microfluidic chips. Furthermore, often the applications dictate that the processes are performed in a gas environment, not allowing the use of a filler liquid (e.g., oil). These properties pose challenges for delivering controlled volumes of liquid to the chip. An automated, simple, accurate and reliable method of delivering reagents from sealed, off-chip reservoirs is presented here. This platform overcomes the issues of evaporative losses of volatile solvents, cross-contamination, and flooding of the chip by combining a syringe pump, a simple on-chip liquid detector and a robust interface design. The impedance-based liquid detection requires only minimal added hardware to provide a feedback signal to ensure accurate volumes of volatile solvents are introduced to the chip, independent of time delays between dispensing operations. On-demand dispensing of multiple droplets of acetonitrile, a frequently used but difficult to handle solvent due to its wetting properties and volatility, was demonstrated and used to synthesize the positron emission tomography (PET) probe [(18)F]FDG reliably.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Electrowetting
  • Fluorodeoxyglucose F18 / chemistry
  • Hydrophobic and Hydrophilic Interactions
  • Microfluidic Analytical Techniques / instrumentation*
  • Positron-Emission Tomography
  • Solvents / chemistry
  • Volatile Organic Compounds / chemistry*


  • Solvents
  • Volatile Organic Compounds
  • Fluorodeoxyglucose F18