ac6b03653_si_001.pdf (451.74 kB)
Cation Dependent Surface Charge Regulation in Gated Nanofluidic Devices
journal contribution
posted on 2016-12-20, 00:00 authored by Marie Fuest, Kaushik K. Rangharajan, Caitlin Boone, A. T. Conlisk, Shaurya PrakashSurface
charge governs nanoscale aqueous electrolyte transport,
both in engineered analytical systems and in biological entities such
as ion channels and ion pumps as a function of ion type and concentration.
Embedded electrodes in a nanofluidic channel, isolated from the fluid
in the channel by a dielectric layer, act as active, tunable gates
to systematically modify local surface charge density at the interface
between the nanochannel surface and the aqueous electrolyte solution,
causing significant changes in measured nanochannel conductance. A
systematic comparison of transport of monovalent electrolytes [potassium
chloride (KCl), sodium chloride (NaCl)], 2:1 electrolytes [magnesium
chloride (MgCl2), calcium chloride (CaCl2)],
and electrolyte mixtures (KCl + CaCl2) through a gated
nanofluidic device was performed. Ion–surface interactions
between divalent Ca2+ and Mg2+ ions and the
nanochannel walls reduced the native surface charge density by up
to ∼4–5 times compared to the monovalent cations. In
electrolyte mixtures, Ca2+ was the dominating cation with
nanochannel conductance independent of KCl concentration. Systematic
changes in local electrostatic surface state induced by the gate electrode
are impacted by the divalent cation–surface interactions, limiting
modulation of the local surface potential by the gate electrode and
resulting in cation dependent nanoscale ion transport as seen through
conductance measurements and numerical models.