Angstrofluidics: Walking to the Limit

Abstract

Angstrom-scale fluidic channels are ubiquitous in nature and play an important role in regulating cellular traffic, signaling, and responding to stimuli. Synthetic angstrom channels are now a reality with the emergence of several cutting-edge bottom-up and top-down fabrication methods. In particular, the use of atomically thin 2D materials and nanotubes as components to build fluidic conduits has pushed the limits of fabrication to the angstrom scale. Here, we provide an overview of recent developments in the fabrication methods for nano- and angstrofluidic channels while categorizing them on the basis of dimensionality (0D pores, 1D tubes, 2D slits), along with the latest advances in measurement techniques. We discuss the ion transport governed by various stimuli in these channels and the variation of ionic mobility, streaming power, and osmotic power with pore size across all the dimensionalities. Finally, we highlight unique future opportunities in the development of smart ionic devices.

Interfacial Liquid Water on Graphite, Graphene, and 2D Materials

“…13,110−113,131−135 Nanofluidic channels made from twodimensional crystals enabled the fabrication of devices that relied on the interfacial liquid water properties. 14,46 Those devices were also applied to study the interaction of water with graphene and hexagonal boron nitride surfaces. 65,136 Water Contact Angle.…”

“…The interaction of liquid water with graphite-like and 2D materials has generated scientific topics, among them, the wetting transparency of graphene, − ,− the water-flow in nanofluidic channels and nanopores, ,− or the ubiquitous presence of organic adsorbates at the graphite–liquid-water interface. ,− ,− …”

Ion-Selective Separation Using MXene-Based Membranes: A Review

“…Furthermore, analogous to biological potassium ion pump, MXene-based membranes showed spontaneous ionic motion under pressure in conjunction with higher K + /Na + selectivity . A literature review reveals that nanoconfined ion transport in stacked MXene membranes can be regulated by external stimuli, suggesting that 2D MXene material-based membranes can be utilized in the future to comprehend and innovate modern ionic devices, such as ionic diodes and pumps. ,− …”

Light-Driven Ion Transport through Single-Heterojunction Nanopores

“…I on transport plays an important role in the process of signal transfer and energy conversion of living matter, 1−4 arousing the development of artificial ion channels which mimic biological protein channels to achieve specific functionalities. 5−9 Thanks to recent advances in nanoprocessing technologies, 10−13 synthetic nanofluidic systems can be fabricated now on the atomic length scale 14 to mimic their natural counterparts, thereby facilitating the revelation of anomalous behaviors and mechanisms of ion transport under extremely confined conditions via various manipulation approaches. 15,16 Among a large diversity of methods for controlling ion transport through artificial channels, light as an exogenous regulating method can readily be implemented and rich photoeffects can be employed for designing multiple functions, which offers a new dimension for ion transport manipulation.…”

“…Ion transport plays an important role in the process of signal transfer and energy conversion of living matter, − arousing the development of artificial ion channels which mimic biological protein channels to achieve specific functionalities. − Thanks to recent advances in nanoprocessing technologies, − synthetic nanofluidic systems can be fabricated now on the atomic length scale to mimic their natural counterparts, thereby facilitating the revelation of anomalous behaviors and mechanisms of ion transport under extremely confined conditions via various manipulation approaches. , Among a large diversity of methods for controlling ion transport through artificial channels, light as an exogenous regulating method can readily be implemented and rich photoeffects can be employed for designing multiple functions, which offers a new dimension for ion transport manipulation . A van der Waals heterojunction can be used to build a variety of functional electronic devices such as solar cells, photoelectric detectors, and photocatalysis based on its light-harvesting capability. , Moreover, such van der Waals stacking devices can be transferred to ionic systems, thus realizing tunable functions also in nanofluidics. − For a natural photosynthesis process, a photoresponsive ion pump relies primarily on biomolecules embedded in the thylakoid membrane of chloroplasts. , To mimic this process, artificial light-induced ion pumping systems employing multiple channels have been shown, though the mechanism has not been fully understood. ,− In contrast, implementation of artificial ion pumping in a single nanopore in a van der Waals heterojunction with ultimate thickness can in principle offer a direct and effective way to access the microscopic vision of the photodriven ion transport, which remains unexplored.…”