Bioinspired nervous signal transmission system based on two-dimensional laminar nanofluidics: From electronics to ionics.

Mammalian nervous systems, as natural ionic circuitries, stand out in environmental perception and sophisticated information transmission, relying on protein ionic channels and additional necessary structures. Prosperously emerged ionic regulated biomimetic nanochannels exhibit great potentialities in various application scenarios, especially signal transduction. Most reported direct current systems possess deficiencies in informational density and variability, which are superiorities of alternating current (AC) systems and necessities in bioinspired nervous signal transmission. Here, inspired by myelinated saltatory conduction, alternating electrostatic potential controlled nanofluidics are constructed with a noncontact application pattern and MXene nanosheets. Under time-variant external stimuli, ions confined in the interlaminar space obtain the capability of carriers for the AC ionic circuit. The transmitted information is accessible from typical sine to a frequency-modulated binary signal. This work demonstrates the potentiality of the bioinspired nervous signal transmission between electronics and ionic nanofluidics, which might push one step forward to the avenue of AC ionics.

Engineering Bio-inspired Self-assembled Nanochannels for Smart Ion Transport.

Highly efficient biological ion channels with sophisticated transport characteristics in living organisms have inspired the design of artificial channels that are functionally comparable to those of their natural counterparts and applicable on a much larger scale. Self-assembly currently offers a facile approach for producing nanoconfined ion channels that exhibit smart ion-transport properties, including ion selectivity, gating, and rectification, and have shown great potential for various applications. In this Minireview, we give an overview of strategies for engineering bio-inspired self-assembled ion channels. We focus on emerging channel assemblies based on different fabrication processes such as supramolecular assembly, nanosystem-based fabrication, and polymer-based integration. The applications of these bio-inspired channels in the exploration of physiological events, detection of molecules/ions, ion separation, and energy conversion are concisely presented. Finally, future developments and challenges of this booming research field are proposed.

Light-Driven ATP Transmembrane Transport Controlled by DNA Nanomachines.

In nature, biological machines can perform sophisticated and subtle functions to maintain the metabolism of organisms. Inspired from these gorgeous works of nature, scientists have developed various artificial molecular motors and machines. However, selective transport of biomolecules across membrane has remained a great challenge. Here, we establish an ATP transport system by assembling photocontrolled DNA nanomachines into the artificial nanochannels. With alternant light irradiation, these ATP transport lines can selectively shepherd cargoes across the polymer membrane. These findings point to new opportunities for manipulating and improving the mass transportation and separation with light-controlled biomolecular motors, and can be used for other molecules and ions transmembrane transport powered by light.

Bioinspired Heterogeneous Ion Pump Membranes: Unidirectional Selective Pumping and Controllable Gating Properties Stemming from Asymmetric Ionic Group Distribution.

The creation of an artificial solid-state ion pump that mimics the delicate ion transport behaviors of a biological protein-based ion pump is drawing more and more research attention due to its potential applications in energy conversion, biosensor, and desalination. However, the reported bioinspired double-gated ion pump systems are generally very primary and can only realize nonselective ion pumping functions with no directionality and uncontrollable ion gating functions, which are far from their biological counterparts. To make the bioinspired device "smart" in a real sense, the implementation of high-level selectivity and directionality in the ion pumping process, while achieving great controllability in the ion gating process, is a necessity. Here, we developed a bioinspired heterogeneous ion pump membrane by combining block copolymer membrane sacrificial coating and plasma grafting technique. The system has unidirectional selective ion pumping and controllable ion gating properties. The introduction of asymmetric ionic group distribution is the key reason for its novel transport behaviors. Such a heterogeneous ion pump could not only provide a basic platform that potentially sparks further efforts to simulate the smart ion transport processes in living bodies but also promote the application of artificial nanofluidic devices in energy conversion, water treatment, and biosensing.

Light-Controlled Ion Transport through Biomimetic DNA-Based Channels.

Light-controlled nanochannels are fabricated through self-assembling azobenzene-incorporated DNA (Azo-DNA) strands to regulate ion transport. By switching between collapsed and relaxed states using visible and ultraviolet light alternately, the Azo-DNA channels can be opened and closed because the conformation of Azo-DNA changes, that is, Azo-DNA is used as switchable controlling unit. In addition to sharing short response time and reversibility with other photoresponsive apparatuses, the Azo-DNA-based nanochannel system has advantages in good biocompatibility and versatile design, which could potentially be applied in light-controlled drug release, optical information storage, and logic networks.

Construction of biomimetic smart nanochannels with polymer membranes and application in energy conversion systems.

Learning from nature has inspired the creation of intelligent devices to meet the increasing needs of the advanced community and also to better understand how to imitate biology. As one of biomimetic nanodevices, nanochannels or nanopores aroused particular interest because of their potential applications in nanofluidic devices, biosensing, filtration, and energy conversions. In this review we have summarized some recent results mainly focused on the design, construction and application in energy conversion systems. Like biological nanochannels, the prepared smart artificial nanochannels fabricated by ion track-etched polymer membranes and smart molecules show a great potential in the field of bioengineering and biotechnology. And these applications can not only help people to know and understand the living processes in nature, but can also inspire scientists to study and develop novel nanodevices with better performance for the mankind.

Ultra-Sensitive and Selective Electrochemical Bio-Fluid Biopsy for Oral Cancer Screening.

The early diagnosis of recurrence and metastasis is critically important for decreasing the morbidity and mortality associated with oral cancers. Although liquid biopsy methods hold great promise that provide a successive "time-slice" profile of primary and metastatic oral cancer, the development of non-invasive, rapid, simple, and cost-effective liquid biopsy techniques remains challenging. In this study, an ultrasensitive and selective electrochemical liquid biopsy is developed for oral cancer screening based on tracking trace amounts of cancer biomarker by functionalized asymmetric nano-channels. Detection via antigen-antibody reactions is assayed by evaluating changes in ionic current. Upon the recognition of cancer biomarker antigens in bio-fluids, the inner wall of nano-channel immobilized with the corresponding antibodies undergoes molecular conformation transformation and surface physicochemical changes, which significantly regulate the ion transport through the nano-channel and help achieve sensitivity with a detection limit of 10-12 g mL-1 . Furthermore, owing to the specificity of the monoclonal antibody for the antigen, the nano-channel exhibits high selectivity for the biomarker than for structurally similar biological molecules present in bio-fluids. The effectiveness of this technique is confirmed through the diagnosis of clinical cases of oral squamous cell carcinoma. This study presents a novel diagnostic tool for oral cancer detection in bio-fluids.

Biomimetic Nacre-Like Silk-Crosslinked Membranes for Osmotic Energy Harvesting.

As an approach to harvesting sustainable energy from ambient conditions, the osmotic energy between river water and seawater contributes to solving global issues such as the energy shortage and environmental pollution. Current attempts based on a reverse electrodialysis technique are limited mainly due to the economically unviable power density and inadequate mass transportation of membrane materials. Here, we demonstrate a benign strategy for designing a multilayer graphene oxide-silk nanofiber-graphene oxide biomimetic nacre-like sandwich as an osmotic power generator. Enhanced interfacial bonding endows the composite membranes with long-term stability in saline, and meanwhile, the two-dimensional nanofluidic channel configuration also reduces the ion transport resistance and provides large storage spaces for ions. Thus, the output power density of the proposed membrane-based generator achieves a value of up to 5.07 W m-2 by mixing seawater and river water. Furthermore, we experimentally and theoretically demonstrate that the thermal-field drives the increased output power density due to the advances in ionic movement range and activity of electrode reaction, showing the promise of strengthened thermo-osmotic energy conversion.

Artificial light-driven ion pump for photoelectric energy conversion.

Biological light-driven ion pumps move ions against a concentration gradient to create a membrane potential, thus converting sunlight energy directly into an osmotic potential. Here, we describe an artificial light-driven ion pump system in which a carbon nitride nanotube membrane can drive ions thermodynamically uphill against an up to 5000-fold concentration gradient by illumination. The separation of electrons and holes in the membrane under illumination results in a transmembrane potential which is thought to be the foundation for the pumping phenomenon. When used for harvesting solar energy, a sustained open circuit voltage of 550 mV and a current density of 2.4 µA/cm2 can reliably be generated, which can be further scaled up through series and parallel circuits of multiple membranes. The ion transport based photovoltaic system proposed here offers a roadmap for the development of devices by using simple, cheap, and stable polymeric carbon nitride.

A Bioinspired Multifunctional Heterogeneous Membrane with Ultrahigh Ionic Rectification and Highly Efficient Selective Ionic Gating.

A bioinspired multifunctional heterogeneous membrane composed of a block copolymer (PS-b-P4VP) membrane and a porous anodic alumina membrane is fabricated. The ionic rectification is so strong that the maximum ratio is ≈489, and the chemical actuation of the anion or cation gate from the "OFF" to the "ON" state promotes a 98.5% increase in the channel conductance.

Engineered Asymmetric Composite Membranes with Rectifying Properties.

Asymmetric composite membranes with rectifying properties are developed by grafting pH-stimulus-responsive materials onto the top layer of the composite structure, which is prepared by two novel block copolymers using a phase-separation technique. This engineered asymmetric composite membrane shows potential applications in sensors, filtration, and nanofluidic devices.

Chiral recognition of L-tryptophan with beta-cyclodextrin-modified biomimetic single nanochannel.

A stable system of enantioselectively recognising L-tryptophan based on ß-cyclodextrin-modified single nanochannel fabricated in a polyimide membrane was demonstrated, and we realized the chiral recognition of an essential amino acid with this system for the first time.

A biomimetic zinc activated ion channel.

A novel biomimetic zinc activated ion channel was prepared by incorporating a zinc responsive peptide, zinc finger, into a single polymeric nanochannel.