Nonequilibrium Ionic Response of Biased Mechanically Controllable Break Junction (MCBJ) Electrodes

Abstract

Novel experimental techniques allow for the manipulation and interrogation of biomolecules between metallic probes immersed in micro/nanofluidic channels. The behavior of ions in response to applied fields is a major issue in the use of these techniques in sensing applications. Here, we experimentally and theoretically elucidate the behavior of background currents in these systems. These large currents have a slowly decaying transient response, as well as noise that increases with ionic concentration. Using mechanically controllable break junctions (MCBJ), we study the ionic response in nanogaps with widths ranging from a few nanometers to millimeters. Moreover, we obtain an expression for the ionic current by solving time-dependent Nernst–Planck and Poisson equations. This expression shows that after turning on an applied voltage, ions rapidly respond to the strong fields near the electrode surface, screening the field in the process. Ions subsequently translocate in the weak electric field and slowly relax within the diffusion layer. Our theoretical results help to explain the short- and long-time behavior of the ionic response found in experiments, as well as the various length scales involved.

Electrohydrodynamic Flow through a 1 mm2 Cross-Section Pore Placed in an Ion-Exchange Membrane

“…This point has already been discussed in a previous study. 22 As shown in Figure 10a, a measured electric signal was fitted by linear combinations of some exponents considering the time constants of τ e = 0.01, 0.1, 1, and 10 s. Using these constants, experimental data could be fitted by …”

Development of glass micro-electrodes for local electric field, electrical conductivity, and pH measurements

“…Numerical analysis of electric fields in the channel. Electrical potential distributions were numerically evaluated by solving the Nernst-Planck and Poisson equations 18,50 . The electrostatic potential is related to the electrical charge density as follows:…”

“…Some numerical studies predicted an potential difference in electrolyte solutions as a function of ion concentration [14][15][16][17] . By solving the Nernst-Planck and Poisson equations, the relationship between the electrical potential and the concentration was clarified 18,19 . In particular, an electrode surface is strongly screened by electrolyte ions that form an electric double layer (EDL), and thus the applied electrical potential usually decreases near the surface.…”

Characterizing molecular junctions through the mechanically controlled break-junction approach

“…Recently, Doi et al reported on the transient electrical response of ions in the vicinity of biased electrodes. 106 Their results showed that ions rapidly responded to the strong fields near the electrode surface after turning on an applied voltage that screened the field in the process. Ions subsequently translocated in the weak electric field, and slowly relaxed within the diffusion layer.…”