Cation dependent electroosmotic flow in glass nanopores

Abstract

We present our findings on the changes to electroosmotic flow outside glass nanopores with respect to the choice of Group 1 cation species. In contrast with standard electrokinetic theory, flow reversal was observed for all salts under a negative driving voltage. Moving down Group 1 resulted in weaker flow when the driving voltage was negative, in line with the reduction in the zeta potential on the glass surface going down the periodic table. No trend emerged with a positive driving voltage, however for Cs, flow was uniquely found to be in reverse. These results are explained by the interplay between the flow inside the nanopore and flow along the outer walls in the vicinity of the nanopore.Nanopores are sensors based on the resistive-pulse technique 1 . Sensing is achieved by monitoring the ionic current through a nanoscale aperture in electrolytic solution. Nanopores exist in a variety of forms, the earliest used for sensing being the biological nanopore α-haemolysin 2,3 . Today many solid state nanopore systems are known, primary examples of these being Si 3 N 4 4 , quartz glass 5 and graphene 6 . They have all proven capable of single molecule sensing 7 , detecting proteins 8,9 , DNA sequencing 10 and, in conjunction with DNA nanotechnology, detection of single nucleotide polymorphisms 11 and specific proteins from mixtures 12 .Hydrodynamic and electrokinetic phenomena dictate the behavior of analytes in nanopores. There are many works theoretically and experimentally probing the details of these phenomena with regards to micro-and nanofluidic systems [13][14][15][16] . Here, of prime importance is electroosmosis. Si 3 N 4 and glass nanopores have a negative surface charge in solution at biological pH. This results in a build-up of positive ions proximate to the surface 17 . Applying an electric field to drive an analyte through a nanopore causes the charges at the surface to move. The moving charges couple to the fluid medium and result in electroosmotic flow (EOF). This effect is depicted in Fig. 1(a). The force a target molecule experiences in nanopores thus depends sensitively on the direction and strength of EOF 18,19 ; it may slow the target down in a manner useful for sensing, or it may deny entry to molecules, hampering throughput 18,20,21 . As such, EOF in nanopores has been extensively studied 22-24 , including reports of enhancement of molecular binding within an α-haemolysin nanopore with EOF 25 , facilitated protein capture in Fragaceatoxin C nanopores using EOF 26 , and recently the demonstration that EOF can be used to control the folding state of DNA entering glass nanopores 27 .Applying an electric field through the nanopore not only drives flow from within the pore, it establishes a flow field in the region outside the pore that is several microns a) Email: ufk20@cam.ac.uk in extent. This field can be quantified by a single parameter, P , the force required to generate this field in an otherwise calm fluid. This force originates from an immersed fluid jet which is described by the Landau-Sq...

Nanopore electro-osmotic trap for the label-free study of single proteins and their conformations

“…1a), which results in a strong hydrodynamic flux towards the pore. This nanofluidic effect is called electro-osmosis and is well studied in the context of surface charge in nanochannels and nanopores [15][16][17][18] (see also Supplementary Notes 3.1). Here, however, the electro-osmosis is not surface driven -as the lipid bilayer surface is net neutral -but induced site-specifically by the DNA origami structure that acts as a nanoporous negatively charged sponge.…”

Effective cell membrane tension is independent of polyacrylamide substrate stiffness

“…OT measurements took place on a custom-built inverted microscope 34 . Briefly, a 5 W 1064 nm ytterbium fibre laser (YLM-5-LP, IPG Laser, Germany) was used at a high power (> 1 W) to minimize intensity fluctuations.…”

Constricted Apertures for Dynamic Trapping and Micro-/Nanoscale Discrimination Based on Recapture Kinetics

“…The conditions for pressure-dominated translocation of micro- and nanoscale objects will also be discussed. Critical to this discussion is how the applied voltage impacts the recapture and should be compared to existing literature on electric-field induced motion of particles inside micro and nanopores. − …”