Bipolar Ionic Diode with a Transformable Polyelectrolyte Network for High-Efficiency Ion Transport and Enhanced...

Recent studies on ionic diodes for ion transport regulation have shown promising functions with high rectification ratios. However, typical ionic diodes face challenges in attaining high output efficiency and ion flux due to their requirement of nanoscale dimensions for ion selectivity. In this article, we introduce a novel bipolar ionic diode constructed through the combined assembly of nanoparticles and a transformable polyelectrolyte network. Experimental and numerical studies were conducted to characterize and optimize the fabrication parameters, resulting in a remarkable rectification ratio exceeding 1000. The presented ionic diode possesses the unique capability to automatically transform from a dense to a loose structure in response to an applied potential bias. This feature enables high output efficiency and rapid ion accumulation. Leveraging these characteristics, we developed a fluorescence-based sensor with ultrahigh sensitivity for nickel ions, achieving a detection limit of 1 nM with a minimal sample volume of 50 μL─an improvement of 2 orders of magnitude over conventional bulk solutions with the same fluorescence indicator. This ionic diode demonstrates exceptional ability and flexibility in high-efficiency ion transport, positioning itself as a promising platform with broad applications for enhancing sensitivity in various fluorescence-based sensing applications within aqueous environments.