Figure 3.

(a) Model of SECM-induced ion transfer across a nanopore membrane (red dotted line). The black solid lines represent liquid/liquid interfaces with h/a = 0, 0.38, and 0.81 for monovalent ions, Arixtra, and protamine, respectively. The transfer of the target ions across the pipet-supported interface is diffusion-limited. The blue and green lines represent boundaries with zero normal flux and simulation space limits, respectively. The simulation space (light blue) is limited to the external solution surrounded by these boundaries while ion diffusion in the internal solution is not relevant to the tip current. (b) SECM approach curves at a SiO₂ substrate for TBA⁺, Arixtra, and protamine in 0.1 M PBS (solid lines). The probe scan rates are 0.3, 0.23, and 0.23 μm/s, respectively. The circles for the respective ions represent approach curves simulated with impermeable membranes for a = 1.9, 1.8, and 2.0 μm.