The discovery of ionic current rectification (ICR) phenomena in synthetic nanofluidic systems elicits broad interest from interdisciplinary fields of chemistry, physics, materials science, and nanotechnology; and thus, boosts their applications in, for example, chemical sensing, fluidic pumping, and energy related aspects. So far, it is generally accepted that the ICR effect stems from the broken symmetry either in the nanofluidic structures, or in the environmental conditions. Although this empirical regularity is supported by numerous experimental and theoretical results, great challenge still remains to precisely figure out the correlation between the asymmetric ion transport properties and the degree of symmetry breaking. An appropriate and quantified measure is therefore highly demanded. Herein, taking DNA-stuffed nanopores as a model system, we systematically investigate the evolution of dynamic ICR in between two symmetric states. The fully stuffed and fully opened nanopores are symmetric; therefore, they exhibit linear ion transport behaviors. Once the stuffed DNA superstructures are asymmetrically removed from one end of the nanopore via aptamer-target interaction, the nanofluidic system becomes asymmetric and starts to rectify ionic current. The peak of ICR is found right before the breakthrough of the stuffed DNA forest. After that, the nanofluidic system gradually retrieves symmetry, and becomes non-rectified. Theoretical results by both the coarse-grained Poisson-Nernst-Planck model and the 1D statistic model excellently support the experimental observations, and further establish a quantified correlation between the ICR effect and the degree of asymmetry for different molecular filling configurations. Based on the ICR properties, we develop a proof-of-concept demonstration for sensing ATP, termed the ATP balance. These findings help to clarify the origin of ICR, and show implications to other asymmetric transport phenomena for future innovative nanofluidic devices and materials.

Osmotic power generation in biomimetic nanofluidic systems has attracted considerable research interest owing to the enhanced performance and long-term stability. Towards practical applications, when extrapolating the materials from single-nanopore to multi-pore membranes, conventional viewpoint suggests that, to gain high electric power density, the porosity should be as high as possible. However, recent experimental observations show that the commonly-used linear amplification method largely overestimates the actual performance, particularly at high pore density. Herein, we provide a theoretical investigation to understand the reason. We find a counterintuitive pore-density dependence in high porosity nanofluidic systems that, once the pore density approaches more than 1×10 9 pores/cm 2 , the overall output electric power goes down with the increasing pore density. The excessively high pore density impairs the charge selectivity and induces strong ion concentration polarization, which undermines the osmotic power generation process. By optimizing the geometric size of the nanopores, the performance degradation can be effectively relieved. These findings clarify the origin of the unsatisfactory performance of the current osmotic nanofluidic power sources, and provide insights to further optimize the device.

Summary of main observation and conclusion Osmotic power generated by mixing ionic solutions of different concentration is an underutilized clean energy resource that satisfy potentially the ever‐growing energy demand. For decades, substantial efforts are made to enhance the power density. Toward this goal, we once developed a heterogeneous nanoporous membrane comprising of heterojunctions between negatively charged mesoporous carbon and positively charged macroporous alumina to harvest electric power from salinity difference and achieved outstanding performance (J. Am. Chem. Soc. 2014, 136, 12265). The heterogeneous nanopore junction effectively suppresses ion concentration polarization (ICP) at low concentration end, and consequently promotes the overall power density. However, to date, a systematic understanding of the role of the heterogeneous nanopore junction in osmotic energy conversion remains urgent and largely unexplored. Herein, we provide an in‐depth theoretical investigation on this issue with special emphasis on several influential factors, such as the ionic concentration, the surface charge density, and the geometry of heterogeneous part. To balance the suppression of ICP and maintenance of charge selectivity, we find that these influential factors in the heterogeneous part should be restricted to a specific range. These findings provide direct guidance for design and optimization of high‐performance nanofluidic power sources.