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Issue 7, 2013
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Highly reproducible chronoamperometric analysis in microdroplets

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Here we report a method for highly reproducible chronoamperometric analysis of the contents of microdroplets. Aqueous microdroplets having volumes on the order of 1 nL and separated by a fluorocarbon solvent are generated within a microfluidic device using a T-shaped junction. The key finding is that stable and reproducible quasi-steady-state currents are observed if the electrochemical measurements are made in a narrowed segment of a microchannel. Under these conditions, the microdroplets are stretched, here by a factor of 10, leading to desirable intradroplet mass transfer characteristics. Microdroplet frequencies up to 0.67 s−1 are accessible using this method. The quasi-steady-state currents resulting from chronoamperometric analysis of microdroplets containing 1.0 mM Ru(NH3)63+ have relative standard deviations of just 1.8% and 2.8% at flow rates of 30 nL min−1 and 60 nL min−1, respectively. Importantly, the design of the microelectrochemical device ensures direct contact between intradroplet redox molecules and the electrode surface. That is, the fluorocarbon between microdroplets does interfere with inner-sphere electrocatalytic processes such as the oxygen reduction reaction. Finite-element simulations are presented that are in accord with the experimental findings.

Graphical abstract: Highly reproducible chronoamperometric analysis in microdroplets

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The article was received on 16 Nov 2012, accepted on 21 Jan 2013 and first published on 06 Feb 2013

Article type: Paper
DOI: 10.1039/C3LC41263F
Lab Chip, 2013,13, 1364-1370

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    Highly reproducible chronoamperometric analysis in microdroplets

    H. Liu and R. M. Crooks, Lab Chip, 2013, 13, 1364
    DOI: 10.1039/C3LC41263F

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