title: AC Electroosmotic Pumping in Nanofluidic Funnels.
abstract: We report efficient pumping of fluids through nanofluidic funnels when a symmetric AC waveform is applied. The asymmetric geometry of the nanofluidic funnel induces not only ion current rectification but also electroosmotic flow rectification. In the base-to-tip direction, the funnel exhibits a lower ion conductance and a higher electroosmotic flow velocity, whereas, in the tip-to-base direction, the funnel has a higher ion conductance and a lower electroosmotic flow velocity. Consequently, symmetric AC waveforms easily pump fluid through the nanofunnels over a range of frequencies, e.g., 5 Hz to 5 kHz. In our experiments, the nanofunnels were milled into glass substrates with a focused ion beam (FIB) instrument, and the funnel design had a constant 5° taper with aspect ratios (funnel tip width to funnel depth) of 0.1 to 1.0. We tracked ion current rectification by current-voltage (I-V) response and electroosmotic flow rectification by transport of a zwitterionic fluorescent probe. Rectification of ion current and electroosmotic flow increased with increasing electric field applied to the nanofunnel. Our results support three-dimensional simulations of ion transport and electroosmotic transport through nanofunnels, which suggest the asymmetric electroosmotic transport stems from an induced pressure at the junction of the nanochannel and nanofunnel tip.
authors.affiliation: Department of Chemistry, Indiana University , Bloomington, Indiana 47405-7102, United States.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Kneller
authors.affiliation: Department of Chemistry, Indiana University , Bloomington, Indiana 47405-7102, United States.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Haywood
authors.affiliation: Department of Chemistry, Indiana University , Bloomington, Indiana 47405-7102, United States.
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Jacobson
mesh_terms: D004553:Electric Conductivity; D004560:Electricity; D004574:Electromagnetic Fields; D053841:Electroosmosis / Q000295:instrumentation*; D004867:Equipment Design; D017136:Ion Transport; D007477:Ions / Q000737:chemistry; D056656:Lab-On-A-Chip Devices
chemical_list: D007477:Ions