Hua Dong

A Biomimetic Potassium Responsive Nanochannel: G-Quadruplex DNA Conformational Switching in a Synthetic Nanopore

Potassium is especially crucial in modulating the activity of muscles and nerves whose cells have specialized ion channels for transporting potassium. Normal body function extremely depends on the regulation of potassium concentrations inside the ion channels within a certain range. For life science, undoubtedly, it is significant and challenging to study and imitate these processes happening in living organisms with a convenient artificial system. Here we report a novel biomimetic nanochannel system which has an ion concentration effect that provides a nonlinear response to potassium ion at the concentration ranging from 0 to 1500 microM. This new phenomenon is caused by the G-quadruplex DNA conformational change with a positive correlation with ion concentration. In this work, G-quadruplex DNA was immobilized onto a synthetic nanopore, which undergoes a potassium-responsive conformational change and then induces the change in the effective pore size. The responsive ability of this system can be regulated by the stability of G-quadruplex structure through adjusting potassium concentration. The situation of the grafting G-quadruplex DNA on a single nanopore can closely imitate the in vivo condition because the G-rich telomere overhang is attached to the chromosome. Therefore, this artificial system could promote a potential to conveniently study biomolecule conformational change in confined space by the current measurement, which is significantly different from the nanopore sequencing. Moreover, such a system may also potentially spark further experimental and theoretical efforts to simulate the process of ion transport in living organisms and can be further generalized to other more complicated functional molecules for the exploitation of novel bioinspired intelligent nanopore machines.

Electrospun porous structure fibrous film with high oil adsorption capacity.

A low-cost, high-oil-adsorption film consisting of polystyrene (PS) fibers is fabricated by a facile electrospinning method. Different fiber diameter and porous fibers surface morphology play roles in oil adsorption capacity and oil/water selectivity. The results showed that oil adsorption capacity of PS oil sorbent film with small diameter and porous surface structure for diesel oil, silicon oil, peanut oil and motor oil were approximate to 7.13, 81.40, 112.30, and 131.63 g/g, respectively. It was higher than normal fibrous sorbent without any porous structure. The thinner porous PS oil sorbent also had excellent oil/water selectivity in the cleanup of oil from water.

A pH-Gating Ionic Transport Nanodevice: Asymmetric Chemical Modification of Single Nanochannels

2010 WILEY-VCH Verlag Gmb Ion channels that regulate ion permeation through cell membranes are very important for the implementation of various significant physiological functions in life processes. The components of these channels are asymmetrically distributed between membrane surfaces. Inspired by these asymmetrical nanochannels – including both the various components of ion channels that are not uniform in distribution and the structural asymmetry – the generation of artificial nanochannels has strong implications for the simulation of the different ionic transport processes as well as the enhancement of the functionality of biological ion channels. Recently, we and others have successfully developed simple and functional pH-controllable nanochannels. Here, we further develop the concept of a smart nanochannel system, which is not subject to the solution environment restriction of the chemical modification, by using a plasma asymmetric chemical modification approach. Compared to other systems, this responsive nanochannel system has the advantage that it provides simultaneous control over the pH-tunable asymmetric and pH gating ionic transport properties. This highly effective method can be used in the near future to build smarter, biologically inspired nanochannel machines with more precisely controlled functions by designing more complicated functional molecules. There has been rapid progress in developing chemical properties and chemical modification of the interior surface of the nanochannels with functional molecules, such as specific ions, light, pH, and temperature. In order to achieve different functionalities of artificial nanochannels, various methods have been invented, such as electroless deposition, solution chemical modification, electrostatic self-assembly and to only cover the whole inner surface of the nanochannels. Plasma technology, which mainly includes plasma etching and plasma modification, offers an effective method for nanoscale surface engineering of materials. Plasma etching has often been used in template synthesis of nanomaterials. Plasma modification can functionalize a specific local area precisely, whether via symmetric or asymmetric chemical modification. This advantage can provide the potential variety of nanoscale features and new properties for developing advanced nanomaterials. Even though multiple nanochannel membranes using plasma modification have been studied for the control of the water permeability of polymeric membranes, we still need an optimal system, such as a single nanochannel system, for studying transport properties of different ionic or molecules in a confined space, without having to average the effects of multiple channels. Therefore, in this work, we developed a perfect pH gating ionic transport nanodevice using plasma asymmetric chemical modification, and this approach can be considered as a platform for developing more ways of the precise asymmetric chemical modification of the interior surface of nanochannels, which have strong implications for the simulation of different ionic transport processes as well as the enhancement of ion channel functionality. As shown in Figure 1, we prepared a single nanochannel membrane with the well-developed ion track etching technology. In this work the etched single nanochannel is symmetric and hour-glass shaped (see Supporting Information, Fig. S1). Diameter measurements of hour-glass shaped nanochannels were conducted with a commonly used electrochemical method. The opening at the base was usually 250–300 nm wide and the narrow center (tip) was 10–30 nm wide. Only one side of the nanochannel was treated by plasma-induced grafting in the vapor phase of the distilled acrylic acid (AAc), which became a pH-responsive polymer, poly acrylic acid (PAA), after plasma-induced graft polymerization. To explore the surface properties of the PET films before and after plasma treatment, the films have been studied by contact angle (CA) measurements. The CA of the PET film (Hostaphan RN12 Hoechst, 12mm thick) surfaces after plasma treatment (Fig. 2b) was smaller than the one before treatment (Fig. 2a). The results of the CA measurements showed that the plasma treatment could lead to a visible change of the surface wettability (from 66.68 1.38 to 36.78 6.98), which indicated a change of the chemical composition. This result may spark further experimental approaches to study the relationship between the wettability and ionic transport properties within a confined space at the nanoscale. PAA is a weak polyelectrolyte that adopts a coiled conformation dependant upon the degree of dissociation or protonation, which is controlled by the pH and ionic strength of the surrounding solution, due to ionic repulsion between anionic groups. PAA contains carboxylic groups that become ionized at pH values above its pKa of 4.7 (Fig. 1). [14a] The conformation of this weak polyelectrolyte changes from coiled at low pH to stretched at high pH. The effect of pH on chain conformation on the surface is schematically outlined in Figure 1 (right insert). At low pH values the formation of intramolecular hydrogen bonds in PAA prevails,

Unidirectional water-penetration composite fibrous film via electrospinning

An interesting “water diode” film is fabricated by a facile electrospinning technique. The fibrous film is a composite of hydrophobic polyurethane (PU) and hydrophilic crosslinked poly (vinyl alcohol) (c-PVA) fibrous layers. By taking advantages of the hydrophobic–hydrophilic wettability difference, water can penetrate from the hydrophobic side, but be blocked on the hydrophilic side.

Fabrication of Stable Single Nanochannels with Controllable Ionic Rectification

The fabricationof artificial nanochannels is becominga focus of attentionbecause, comparedwith theirbiological counterparts, they offer flexibility in terms of shape, size, and surface properties for real-world applications. At present, there are several approaches to building single nanochannels (nanopores), such as ion-beam sculpting of Si3N4 membranes, [3] Si/ SiO2 membrane shrinking in transmission electron microscopy, electrochemical etching of glass membranes, and chemical etching of single-track polymer membranes. Because the nanochannel is small enough for interactions between the channel surface and chemical species in the solution, the chemical modification of the nanochannel surface confers great flexibility in developing functional nanochannel materials. Even though several solution methods of coating nanochannels with functional molecules, which enable the size and ion-transport properties of the nanochannels to be easily tuned, have been developed during the past few years, how to endow nanochannels with asymmetric chemical properties is still a challenging task. The chemical properties and chemical modification of artificialnanochannels arecritical components in theadvance of smart functional nanochannels that are tunable by ambient stimuli, such as specific ions, applied force, light, pH, and compression. Recently, the ionic-current rectification of a single nanochannel prepared by the ion-track-etching technique has been studied in comparison with the properties of various ion channels. In those studies, the surface properties of the nanochannel wall are significant for the

Fabrication of Hierarchically Porous Inorganic Nanofibers by a General Microemulsion Electrospinning Approach

One-dimensional nanostructured inorganic oxides have drawn considerable attention in recent years due to their excellent performance, which is superior to that of bulk materials. [ 1 ] Since the interior structure plays an important role in determining the material properties, various 1D nanomaterials with complex inner structures have been fabricated, such as hollow structures, [ 2 ] multilevel structures, [ 3 ] and many other special morphologies and shapes. In particular, much interest has been devoted to porous 1D nanomaterials [ 4 ]

Bioinspired Electrospun Knotted Microfibers for Fog Harvesting

Water is one of the most important substances in life. For most living creatures, water can be obtained from a readily available water source. However, for some others living far away from a water source, water collection becomes an important part of their lives. For example, in the dry Namib Desert, desert beetles live through collecting water from foggy air based on the micrometer-sized patterns of hydrophobic and hydrophilic regions on their backs. With special structures consisting of periodic spindle-knots, spider silks are also endowed with water collecting properties due to the directional moving of water drops from joints to spindle-knots. To adapt to living environment, natural creatures have evolved various elaborate biomaterials with superior performances. Learning from nature is thereby a shortcut for designing new functional materials. Realization of artificial fog-harvesting materials, which could collect water from humid air, will provide a potential outlet to relieve drought in dry areas. Inspired by desert beetles, a number of hydrophobic surfaces with alternative hydrophilic patterns that show fog-collection properties, have been developed up to now. However, the preparation of these materials is relatively cumbersome and costly, which obstructs their spread and application. In previous work, using a dip-coating method, we have fabricated a kind of knotted microfiber which is similar to spider silk in shape. Tiny water drops could be directionally moved and collected on the fiber. Comparing to plate materials, fabric fog-collection materials are undoubtedly more economical in terms of materials and more widely applicable. However, using the earlier method, only a limited length of fiber could be treated at a time. The fabrication of artificial water-collection fibers on a large scale is still challenging. Using electrohydrodynamics to stretch a viscous liquid into fibers (called electrospining) or break a dilute liquid into tiny droplets (called electrospray) has become an effective avenue to generate microscopic materials. Among diverse electrohydrodynamics products, beaded fibers, which are an intermediate state between electrospinning and electrospray products, are normally regarded as unwanted by-product to be avoided as far as possible. However, it has been noticed that the beaded fibers have a structure of periodic knots, which resembles the shape of natural spider silk to some extent. Although some researchers have investigated the fabrication of beaded fibers by electrospinning, few of them have paid attention to the functionality of the unique beaded structures. Recently, we have fabricated a kind of humidity-sensitive heterostructured beaded fiber by coaxial electrospinning. On such a beaded fiber, the main fiber is composed of polystyrene (PS), on which beads composed of polyethylene glycol (PEG) are dispersed. Since PEG is sensitive to water, those beads could reversibly swell and shrink in different humidity. However, this fiber is inapplicable for water collection because PEG is water-soluble. Herein, we fabricated a kind of knotted microfiber able to collect water. On this fiber, PS acts as supporting fiber on which balsam-pear-like poly(methyl methacrylate) (PMMA) knots are distributed. The spindle-knotted structure of this fiber endowed it a surface energy gradient between spindle-knots and joints. When tiny water drops condense on the fiber, they move directionally from the joints to spindle-knots in the same fashion as the water-collecting process on natural spider silk. The electrospinning fabrication of the knotted fibers provides an efficient and low-cost alternative for largearea preparation of water-collection fibers. Coaxial electrospinning (co-ESP) is a powerful approach to fabricate various microscopic core–shell or tubular fibers from various materials. In traditional co-ESP process, a highly viscous solution is used as outer solution in order to form a uniform liquid shell restricting the inner solution. It thus forms core–shell structured thin fibers after the composite liquid thread solidifies. This is a dynamic process in which the viscoelasticity must overwhelm the Rayleigh instability of the shell solution. If the Rayleigh instability cannot be overwhelmed, the thin liquid thread will fluctuate into knotted fiber or even break up into core–shell particles. Most of the earlier studies concentrated on the inhibition of Rayleigh instability in the coESP process to fabricate uniform fabric materials. Herein, however, we intend to employ the Rayleigh instability effect to generate spindle-knots on fibers. We used a viscous PS solution as inner solution, and a dilute PMMA solution as outer solution (Figure 1a). With co-ESP, the inner PS solution was stretched and formed fibers, and the outer PMMA solution flowed out with the inner solution and adhered to the surface of PS fiber. Because of the low concentration and low viscosity of PMMA solution, the liquid film formed a series of liquid drops induced by Rayleigh–Taylor instability before the solvent [a] Dr. H. Dong, Dr. L. Wang, Dr. H. Bai, Prof. L. Jiang Beijing National Laboratory for Molecular Sciences (BNLMS) Key Laboratory of Organic Solids Institute of Chemistry Chinese Academy of Sciences Beijing 100190 (P.R. China) E-mail : jianglei@iccas.ac.cn [b] Dr. N. Wang, Dr. J. Wu, Prof. Y. Zheng, Prof. Y. Zhao Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education School of Chemistry and Environment Beihang University Beijing 100191 (P.R. China) E-mail : zhaoyong@iccas.ac.cn [c] Dr. H. Dong, Dr. L. Wang, Dr. H. Bai Graduate University of Chinese Academy of Sciences Beijing 100039 (P.R. China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cphc.201100957.

Assembly of F0F1-ATPase into solid state nanoporous membrane

A novel ATPase/nanoporous membrane system was prepared. In this system, the activity of F(0)F(1)-ATPase was preserved. The two sides of F(0)F(1)-ATPase were successfully separated macroscopically, and the chemical environments of the two sides could be manipulated in situ individually and freely. Furthermore, this system was also provided with mobility and reusage.

Acrylic acid grafted porous polycarbonate membrane with smart hydrostatic pressure response to pH

A smart “pH-hydrostatic pressure responsor” is fabricated by plasma-induced graft polymerization. Acrylic acid was grafted onto a polycarbonate porous membrane. By taking advantage of the conformational changes of polyacrylic acid chains in acidic and alkaline solutions, the grafted membrane exhibits hydrostatic pressure variation and reversible conversion to pH.

Scab-Inspired Cytophilic Membrane of Anisotropic Nanofibers for Rapid Wound Healing

This work investigates the influence of cytophilic and anisotropic nanomaterials on accelerated cell attachment and directional migration toward rapid wound healing. Inspired by the anisotropic protein nanofibers in scab, a polyurethane (PU) nanofibrous membrane with an aligned structure was fabricated. The membrane showed good affinity for wound-healing-related cells and could guide cell migration in the direction of PU nanofibers. Also, the morphology and distribution of F-actin and paxillin of attached cells were influenced by the underlying nanofibers. The randomly distributed PU nanofibers and planar PU membrane did not show a distinct impact on cell migration. This scab-inspired cytophilic membrane is promising in applications as functional interfacial biomaterials for rapid wound healing, bone repair, and construction of neural networks.