The osmotic energy, as a representative of sustainable clean energy, has provided promising strategies to the energy shortage and the environmental pollution. Via selectively diffusing (cations or anions) through the porous membrane, the osmotic energy can be converted into electricity directly. Nevertheless, the energy-conversion efficiency is significantly limited in the lower surface charge at the membrane surface. In response, here a novel gate-controlled nanopore (field effect transistor-like) as an efficient osmotic generator is exploited. With real-time application of negative gate voltages, the surface charge density is accurately enhanced by an order of magnitude from −0.01 to −0.1 C m⁻² while maintaining an effective salinity difference. Based on that, the single-pore osmotic power is amazingly boosted by four orders of magnitude, reaching the summit of 2.90 nW, which outperforms the state-of-the-art 2D system represented by single-layer MoS₂ of 1 nW. Further expanding into porous membranes, the corresponding power density reaches the pioneering of 1008 W m⁻², far more exceeding the commercial standard of 5 W m⁻². Obviously, this work gives an underlying insight into ionic transport in confined nanochannels, as well as providing an alternative template for efficient osmotic energy generation.

Solid-state nanopores attract widespread interest, owning to outstanding robustness, extensive material availability, as well as capability for flexible manufacturing. Bioinspired solid-state nanopores further emerge as potential nanofluidic diodes for mimicking the rectification progress of unidirectional ionic transport in biological K⁺ channels. However, challenges that remain in rectification are over-reliance on complicated surface modifications and limited control accuracy in size and morphology. In this study, suspended Si₃N₄ films of only 100 nm thickness are used as substrate and funnel-shaped nanopores are controllably etched on that with single-nanometer precision, by focused ion beam (FIB) equipped with a flexibly programmable ion dose at any position. A small diameter 7 nm nanopore can be accurately and efficiently fabricated in only 20 ms and verified by a self-designed mathematical model. Without additional modification, funnel-shaped Si₃N₄ nanopores functioned as bipolar nanofluidic diodes achieve high rectification by simply filling each side with acidic and basic solution, respectively. Main factors are finely tuned experimentally and simulatively to enhance the controllability. Moreover, nanopore arrays are efficiently prepared to further improve rectification performance, which has great potential for high-throughput practical applications such as extended release of drugs, nanofluidic logic systems, and sensing for environmental monitoring and clinical diagnosis.

Nanopores have attracted widespread attention in DNA sequencing and protein or biomarker detection, owning to the single-molecule-scale detection accuracy. Despite the most use of naturally biological nanopores before, solid-state nanopores are widely developed with strong robustness, controllable sizes and geometries, a wide range of materials available, as well as flexible manufacturing. Therefore, various techniques typically based on focused ion beam or electron beam have been explored to drill nanopores directly on free-standing nanofilms. To further reduce and sculpt the pore size and shape for nano or sub-nano space-time sensing precision, various controllable shrinking technologies have been employed. Correspondingly, high-energy-beam-induced contrac-tion with direct visual feedback represents the most widely used. The ability to change the pore diameter was attributed to surface tension induced original material migration into the nanopore center or new material deposition on the nanopore surface. This paper reviews typical solid-state nanopore shrinkage technologies, based on the careful summary of their principles and characteristics in particularly size and morphology changes. Furthermore, the advantages and disadvantages of different methods have also been compared completely. Finally, this review concludes with an optimistic outlook on the future of solid-state nanopores.