Capacitive sensing of droplets for microfluidic devices based on thermocapillary actuation

J.-Z. Chen, A.A. Darhuber, S.M. Troian, S. Wagner

    Research output: Contribution to journalArticleAcademicpeer-review

    80 Citations (Scopus)
    2 Downloads (Pure)

    Abstract

    The design and performance of a miniaturized coplanar capacitive sensor is presented whose electrode arrays can also function as resistive microheaters for thermocapillary actuation of liquid films and droplets. Optimal compromise between large capacitive signal and high spatial resolution is obtained for electrode widths comparable to the liquid film thickness measured, in agreement with supporting numerical simulations which include mutual capacitance effects. An interdigitated, variable width design, allowing for wider central electrodes, increases the capacitive signal for liquid structures with non-uniform height profiles. The capacitive resolution and time response of the current design is approximately 0.03 pF and 10 ms, respectively, which makes possible a number of sensing functions for nanoliter droplets. These include detection of droplet position, size, composition or percentage water uptake for hygroscopic liquids. Its rapid response time allows measurements of the rate of mass loss in evaporating droplets.
    Original languageEnglish
    Pages (from-to)473-480
    Number of pages8
    JournalLab on a Chip
    Volume4
    Issue number5
    DOIs
    Publication statusPublished - 2004

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