title: Characterization and application of controllable local chemical changes produced by reagent delivery from a nanopipet.
abstract: We introduce a versatile method that allows local and repeatable delivery (or depletion) of any water-soluble reagent from a nanopipet in ionic solution to make localized controlled changes in reagent concentration at a surface. In this work, Na(+) or OH(-) ions were dosed from the pipet using pulsed voltage-driven delivery. Total internal reflection fluorescence from CoroNa Green dye in the bath for Na(+) ions or fluorescein in the bath for pH quantified the resulting changes in local surface concentration. These changes had a time response as short as 10 ms and a radius of 1-30 microm and depended on the diameter of the pipet used, the applied voltage, and the pipet-surface separation. After the pipet dosing was characterized in detail, two proof-of-concept experiments on single cells and single molecules were then performed. We demonstrated local control of the sodium-sensitive flagellar motor in single Escherichia coli chimera on the time scale of 1 s by dosing sodium and monitoring the rotation of a 1 microm diameter bead fixed to the flagellum. We also demonstrated triggered single-molecule unfolding by dosing acid from the pipet to locally melt individual molecules of duplex DNA, as observed using fluorescent resonance energy transfer.
authors.affiliation: Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK.
authors.forename: Joe D
authors.initials: JD
authors.lastname: Piper
authors.forename: Chao
authors.initials: C
authors.lastname: Li
authors.forename: Chien-Jung
authors.initials: CJ
authors.lastname: Lo
authors.forename: Richard
authors.initials: R
authors.lastname: Berry
authors.forename: Yuri
authors.initials: Y
authors.lastname: Korchev
authors.forename: Liming
authors.initials: L
authors.lastname: Ying
authors.forename: David
authors.initials: D
authors.lastname: Klenerman
mesh_terms: D000143:Acids; D000468:Alkalies; D035843:Biomedical Research / Q000295:instrumentation / Q000379:methods*; D004247:DNA; D004926:Escherichia coli / Q000737:chemistry; D005407:Flagella; D031541:Fluorescence Resonance Energy Transfer; D005456:Fluorescent Dyes; D012964:Sodium; D017186:Titrimetry; D014894:Weights and Measures
chemical_list: D000143:Acids; D000468:Alkalies; D005456:Fluorescent Dyes; D004247:DNA; D012964:Sodium