title: Bipolar electrode focusing: faradaic ion concentration polarization.
abstract: Bipolar electrode (BPE) focusing locally enriches charged analytes in a microchannel along an electric field gradient that opposes a counter-flow. This electric field gradient forms at the boundary of an ion depletion zone generated by the BPE. Here, we demonstrate concentration enrichment of a fluorescent tracer by up to 500,000-fold. The use of a dual-channel microfluidic configuration, composed of two microchannels electrochemically connected by a BPE, enhances the rate of enrichment (up to 71-fold/s). Faradaic reactions at the ends of the BPE generate ion depletion and enrichment zones in the two, separated channels. This type of device is equivalent to previously reported micro/nanochannel junction arrangements used for ion concentration polarization, but it is experimentally more flexible and much simpler to construct.
authors.affiliation: Department of Chemistry and Biochemistry, Center for Electrochemistry, University of Texas at Austin, 1 University Station, A5300, Austin, Texas 78712-0165, United States.
authors.forename: Robbyn K
authors.initials: RK
authors.lastname: Anand
authors.forename: Eoin
authors.initials: E
authors.lastname: Sheridan
authors.forename: Kyle N
authors.initials: KN
authors.lastname: Knust
authors.forename: Richard M
authors.initials: RM
authors.lastname: Crooks