title: Accurate dispensing of volatile reagents on demand for chemical reactions in EWOD chips.
abstract: 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.
authors: Crump Institute for Molecular Imaging, University of California, Los Angeles, Los Angeles, CA, USA.
authors: Huijiang
authors: H
authors: Ding
authors: Saman
authors: S
authors: Sadeghi
authors: Gaurav J
authors: GJ
authors: Shah
authors: Supin
authors: S
authors: Chen
authors: Pei Yuin
authors: PY
authors: Keng
authors: Chang-Jin C J
authors: CJ
authors: Kim
authors: R Michael
authors: RM
authors: van Dam
mesh_terms: D058874:Electrowetting; D019788:Fluorodeoxyglucose F18 / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation*; D049268:Positron-Emission Tomography; D012997:Solvents / Q000737:chemistry; D055549:Volatile Organic Compounds / Q000737:chemistry*
chemical_list: D012997:Solvents; D055549:Volatile Organic Compounds; D019788:Fluorodeoxyglucose F18