Electricity generated by upstream proton diffusion in two-dimensional nanochannels.

The movement of ions along the pressure-driven water flow in narrow channels, known as downstream ionic transport, has been observed since 1859 to induce a streaming potential and has enabled the creation of various hydrovoltaic devices. In contrast, here we demonstrate that proton movement opposing the water flow in two-dimensional nanochannels of MXene/poly(vinyl alcohol) films, termed upstream proton diffusion, can also generate electricity. The infiltrated water into the channel causes the dissociation of protons from functional groups on the channel surface, resulting in a high proton concentration inside the channel that drives the upstream proton diffusion. Combined with the particularly sluggish water diffusion in the channels, a small water droplet of 5 µl can generate a voltage of ~400 mV for over 330 min. Benefiting from the ultrathin and flexible nature of the film, a wearable device is built for collecting energy from human skin sweat.

High-Resolution and Low-Noise Single-Molecule Sensing with Bio-Inspired Solid-State Nanopores.

Solid-state nanopores have been extensively explored as single-molecule sensors, bearing the potential for the sequencing of DNA. Although they offer advantages in terms of high mechanical robustness, tunable geometry, and compatibility with existing semiconductor fabrication techniques in comparison with their biological counterparts, efforts to sequence DNA with these nanopores have been hampered by insufficient spatial resolution and high noise in the measured ionic current signal. Here we show that these limitations can be overcome by the use of solid-state nanopores featuring a thin, narrow constriction as the sensing region, inspired by biological protein nanopores that have achieved notable success in DNA sequencing. Our extensive molecular dynamics simulations show that these bio-inspired nanopores can provide high spatial resolution equivalent to 2D material nanopores and, meanwhile, significantly inhibit noise levels. A theoretical model is also provided to assess the performance of the bio-inspired nanopore, which could guide its design and optimization.

Proton Coulomb Blockade Effect Involving Covalent Oxygen-Hydrogen Bond Switching.

Instead of the canonical Grotthuss mechanism, we show that a knock-on proton transport process is preferred between organic functional groups (e.g., -COOH and -OH) and adjacent water molecules in biological proton channel and synthetic nanopores through comprehensive quantum and classical molecular dynamics simulations. The knock-on process is accomplished by the switching of covalent O─H bonds of the functional group under externally applied electric fields. The proton transport through the synthetic nanopore exhibits nonlinear current-voltage characteristics, suggesting an unprecedented proton Coulomb blockade effect. These findings not only enhance the understanding of proton transport in nanoconfined systems but also pave the way for the design of a variety of proton-based nanofluidic devices.