Polarization of Gold in Nanopores Leads to Ion Current Rectification

Abstract

Biomimetic nanopores with rectifying properties are relevant components of ionic switches, ionic circuits, and biological sensors. Rectification indicates that currents for voltages of one polarity are higher than currents for voltages of the opposite polarity. Ion current rectification requires the presence of surface charges on the pore walls, achieved either by the attachment of charged groups, or in multi-electrode systems by applying voltage to integrated gate electrodes. Here, we present a simpler concept for introducing surface charges via polarization of a thin layer of Au present at one entrance of a silicon nitride nanopore. In an electric field applied by two electrodes placed in bulk solution on both sides of the membrane, the Au layer polarizes such that excess positive charge locally concentrates at one end and negative charge at the other end. Consequently, a junction is formed between zones with enhanced anion and cation concentrations in the solution adjacent to the Au layer. This bipolar double-layer together with enhanced cation concentration in a negatively charged silicon nitride nanopore leads to voltage-controlled surface-charge patterns and ion current rectification. The experimental findings are supported by numerical modeling that confirm modulation of ionic concentrations by the Au layer and ion current rectification even in low-aspect ratio nanopores. Our findings enable a new strategy for creating ionic circuits with diodes and transistors.

A review: applications of ion transport in micro‐nanofluidic systems based on ion concentration polarization

“…In addition to the ion enrichment applications described above, the ICP principle also has a rectifying effect on the ion current . Rectification is the adjustment of the current pattern.…”

Direct electrochemical observation of glucosidase activity in isolated single lysosomes from a living cell

“…Recently established nanoelectrodes have been implemented to measure the amount of active neurotransmitters inside single vesicles and reactive oxygen/nitrogen species in individual phagolysosomes of living cells ( 12 – 16 ). For even greater function, nanopipettes are coated with carbon, gold, or platinum to fabricate multifunctional nanoring or nanopore electrodes in experiments for intracellular injections, electrical measurements, and electrophysiology ( 17 – 21 ). Single-molecule analysis is achieved by trapping and detection at the tip of a metallic nanopore ( 21 ).…”

Monolayer-gated Ion Transport in Artificial Ion Channels Based on A Nanoporous Gold Membrane

“…Hou 等 [40] 在锥形 PET 单纳米通道的小孔端 沉积纳米颗粒来调控纳米孔的大小, 增强了纳米通道的 离子整流. 最近, Yang 和 Siwy 等 [44] 报道了一种 Au-SiN 纳米通道. 他们首先在 SiN 薄膜上沉积一层金, 然后采 用透射电子显微镜(TEM)下电子束刻蚀将其击穿, 形成 单纳米通道.…”

“…在电场作用下, 纳米通道中 Au 表面发生 极化现象而带有电荷, 从而使纳米通道表现出离子整流 现象. 然而, 目前金纳米通道的制备过程都包括复杂与 昂 贵 的 微 纳 米 加 工 技 术 , 如 重 离 子 轰 击 加 径 迹 刻 蚀 [38～40] 和 TEM 电子束刻蚀 [44] 等. 因此, 有必要发展一 种简单易得的新型金纳米通道.…”