Asymmetric Nanochannel Network-Based Bipolar Ionic Diode for Enhanced Heavy Metal Ion Detection

Abstract

A higher rectification degree in ionic diodes is required to achieve better performance in applications. Nonetheless, the active geometrical change that is critical for inducing electrical potential asymmetry is difficult to realize in typical ionic diodes because of the intrinsic limitation of the fabrication method. Here, we propose a nanochannel-networkbased bipolar diode with a high rectification degree of ∼1600 the highest value realized until now, to the best of our knowledge. Such a high rectification is obtained based on the synergetic effect of the bipolar surface charge and the optimization of the microchannel through experimental studies and multiphysics numerical simulations. It induces ion concentrations at the heterogeneous junction based on the accumulation effect under the forward potential bias. In particular, this proposed molecular concentration occurs in the ohmic region without vortex and instability that is inevitable at the conventional nano-electrokinetic concentration. Combining this accumulation with the horizontally aligned configuration of the nanochannel network membrane (NCNM), a highly sensitive and quantitative mercury ion (Hg 2+ ) sensor based on a fluorescent signal is fabricated that allows direct measurement using a general fluorescent microscope. The detection limit of Hg 2+ is 10 pM, which is ∼10 times lower than the best detection limit realized so far (∼100 pM) in fluorescent dye-based detection. This demonstrates the potential of asymmetric NCNM for high-performance ion transport in applications such as energy conversion, based on its design and material flexibility.

Designing with Iontronic Logic Gates─From a Single Polyelectrolyte Diode to an Integrated Ionic Circuit

“…A more practical realization with a higher R consists of a bipolar diode made of a junction of two oppositely charged ion permselective regions. Surface-functionalized nanochannels, field-effect nanochannels, nanoparticles, and anionic- and cationic exchange membranes (AEM and CEM, respectively) such as polyelectrolytes ,,,− have been used to that end. Under reverse bias, both mobile cations and anions (positively and negatively charged ions, respectively) are depleted from the junction, which results in significantly decreased conductance.…”

Multi‐Control of Ion Transport in a Field‐Effect Iontronic Device based on Sandwich‐Structured Nanochannels

“…[5,6] Nano confinement and surface charge effect underlie the nanofluidic behaviors, and breaking the symmetry of the system can produce ICR. [7][8][9] Artificial nanochannels have many advantages over the biological channels, such as good robustness and sta bility, modifiable surface properties, [10] and the possibility of assembling to circuits, and thus they can be applied to nano fluidic devices, [11] biosensors [12] and energy conversions. [13] To make the system more intelligent, the nanochannels are usually modified with responsive molecules and the ion transportation can be regulated in response to various external stimuli, such as pH, [14,15] light, [16][17][18] temperature, [19,20] electricity [21] and specific molecules/ions.…”

Designing Nanofluidic Diode from a Hybrid‐Bilayer Covalent Organic Framework: Molecular Simulation Investigation

“…As the ionic analog of diodes in solid-state electronics, nanofluidic diodes exhibit unique unidirectional ion currents and rectification effects. They have received considerable interest in a wide variety of applications such as sensing, [1] detection, [2] electronics, [3][4][5] water desalination, [6] and energy conversion. [7,8] Generally, a nanofluidic diode can be formed by an uneven distribution of surface charge potential across a nanopore by rationally tuning pore geometry, surface charge, gated voltage, and ion concentration gradient.…”