Water confined in nanoscale space behaves quite differently from that in the bulk.For example,in biological aquaporins and in carbon nanotubes,the traversing water molecules form a single file configuration.Water would stay in vapor state in extremely hydrophobic narrow nanopores owing to the physicochemical interactions between the water molecules and the surface of the nanopore.A spontaneous wet-dry transition has been identified in both biological and artificial nanopores.The nanopore is either fulfilled with liquid water or completely empty.Based on this mechanism,the wetting and dewetting processes inside nanopores have been further developed into highly efficient nanofluidic gates that can be switched by external stimuli,such as light irradiation,electric potential,temperature,and mechanical pressure.This review briefly covers the recent progress in the special wettability in nanoconfined environment,water transportation through biological or artificial nanochannels,as well as the smart nanofluidic gating system controlled by the water wettability.
Two-dimensional（2 D） nanofluidic systems provide a highly efficient way to integrate a huge amount of cascading lamellar nanofluidic channels into macroscopic membrane materials for practical use in, for example, molecular separation, water treatment, and energy storage. Besides the well-studied graphenebased materials, other 2 D nanomaterials, such as the transition metal dichalcogenides（TMDCs）, are expected as promising alternatives. Here, we report strong ionic current rectification（ICR） effect found in Mo S2/WSe2 bi-layered membrane structure. The preferential direction for ion transport is from the WSe2 layers to the Mo S2 layers. The maximum ICR ratio approaches 35 at intermediate electrolyte concentration. More intriguingly, by exchanging the deposition order of the Mo S2 and WSe2 layers, the observed ICR effect can be reversed. These evidences justify that the highly rectified ion transport phenomenon results from the asymmetry in the reconstructed 2 D layered materials. This work is the first discovery of ICR effect in 2 D nanofluidic heterostructures, and provides further opportunities for innovative nanofluidic devices and materials.
Solid-state nanopores are generally considered as an indispensable element in the research field of fundamental ion transport and molecular sensing. The im- provement in fabrication and chemical modification of the solid-state nanopores remains increasingly updated. During the last decades, numerous works have been reported on the nanopore-based sensing applications. More and more new analytical methods using nanopore-based devices are emerging. In this review, we highlight the recent progress on the analytical methods for the interdisciplinary and fast- growing area of nanopore research. According to the dif- ferent types of the electrical readout, whether it is steady- state ionic current or transient current fluctuation, the nanopore-based sensing and analysis can be generally di- vided into two categories. For the first type, the electrical readout shows a stable blockade or reopening of the nanopore conductance in the presence of target analytes, termed steady-state analysis, including the conductance change, electrochemical analysis, and two-dimensional scanning and imaging. The other type is based on the transient fluctuation in the transmembrane ionic current, termed transient-state analysis, including the noise analysis, transient ion transport, and transverse tunneling current. The investigation of solid-state nanopores for chemical sensing is just in its infancy. For further research work, not only new nanopore materials and chemical modifications are needed, but also other non-electric-based sensing techniques should be developed. We will focus our future research in the framework of bio-inspired, smart, multiscale interfacial materials and extend the spirit of binary cooperative complementary nanomaterials.
There are many elaborate masterpieces exist in natural world. Learning from nature, people developed serial intelligent biomimetic devices. Biomimetic smart nanochannels received widespread attention for mimicking biological processes in bodies. Excellent stability, tailorable surface characteristics and nano-size effects rend polymer single nanochannel an ideal candidate for constructing sensitive and reproducible biosensors. Nanochannels are responsive for special analytes while appropriate recognition elements are modified in channels wall. In this review, we summarized recent works in contructing biosensors that are using polymer single nanochannels for detecting various analytes.
HOU GuangLeiPENG ZhiJianTIAN YeZHANG HuaChengJIANG Lei
