阵列纳米通道中氨基官能团质子化研究

质子化过程是大多数酸碱理论的核心,也发生在许多生命过程中。因此,研究限域环境中分子或官能团的质子化过程将为进一步认识酸碱理论和阐述限域环境中生物分子的基本行为提供理论依据。本文提出了一种以荷电电化学探针检测多孔氧化铝阵列纳米通道内表面官能团质子化过程的新方法。该方法利用纳米通道表面官能团的质子化过程改变了表面荷电性质,从而调控荷电电化学探针在纳米通道中的传输行为。实验中以喷涂在阵列氧化铝纳米通道膜一侧的薄金膜为工作电极,检测通过阵列纳米通道荷电电化学探针的流量,以此获得纳米通道限域条件下的质子化过程。同时以多孔氧化铝阵列纳米通道为限域空腔,利用硅烷化反应将氨基修饰在纳米通道的内表面,通过检测不同pH值条件下铁氰酸根离子在纳米通道中流量的变化,获得了纳米通道限域条件下氨基质子化滴定曲线。结果表明,纳米通道限域条件下氨基官能团发生一步质子化,其pK1/2值为5.9。本文提出的方法适用于研究纳米通道限域条件下其它官能团或生物分子的质子化过程。     

A nanochannel array based device for determination of the isoelectric point of confined proteins

A nanochannel array based nanodevice can mimic the biological environments and thus unveil the natural properties, conformation and recognition information of biomolecules such as proteins and DNA in confined spaces. Here we report that porous anodic alumina (PAA) of a highly parallel nanochannel array covalently modified with proteins significantly modulates the transport of a negatively charged probe of ferricyanide due to the electrostatic interactions between the probes and modified nanochannel inner surface. Results show that such electrostatic interaction exists in a wide range of ionic strength from 1 mM to 100 mM in 20 nm nanochannels modified with proteins (hemoglobin, bovine serum albumin, and goat anti-rabbit IgG secondary antibody). In addition, the maximal steady-state flux of the charged probe through the modified nanochannel array is directly related to the ionic strength which determines the electric double layer thickness and solution pH which modulates the nanochannel surface charge. Thus, the modulated mass transport of the probe by solution pH can be used to study the charge properties of the immobilized proteins in nanochannel confined conditions, leading us to obtain the isoelectric point (pI) of the proteins confined in nanochannels. The determined pI values of two known proteins of hemoglobin and bovine serum albumin are close to the ones of the same proteins covalently modified on a 3-mercaptopropionic acid self-assembled monolayer/gold electrode. In addition, the pI of an unknown protein of goat anti-rabbit IgG secondary antibody confined in nanochannels was determined to be 6.3. Finally, the confinement effect of nanochannels on the charge properties of immobilized proteins has been discussed.     

Biomimetic Ion Nanochannels as a Highly Selective Sequential Sensor for Zinc Ions Followed by Phosphate Anions

A novel biomimetic ion‐responsive multi‐nanochannel system is constructed by covalently immobilizing a metal‐chelating ligand, 2,2′‐dipicolylamine (DPA), in polyporous nanochannels prepared in a polymeric membrane. The DPA‐modified multi‐nanochannels show specific recognition of zinc ions over other common metal ions, and the zinc‐ion‐chelated nanochannels can be used as secondary sensors for HPO₄^2? anions. The immobilized DPA molecules act as specific‐receptor binding sites for zinc ions, which leads to the highly selective zinc‐ion response through monitoring of ionic current signatures. The chelated zinc ions can be used as secondary recognition elements for the capture of HPO₄^2? anions, thereby fabricating a sensing nanodevice for HPO₄^2? anions. The success of the DPA immobilization and ion‐responsive events is confirmed by measurement of the X‐ray photoelectron spectroscopy (XPS), contact angle (CA), and current–voltage (I–V) characteristics of the systems. The proposed nanochannel sensing devices display remarkable specificity, high sensitivity, and wide dynamic range. In addition, control experiments performed in complex matrices suggest that this sensing system has great potential applications in chemical sensing, biotechnology, and many other fields.     

Metal-macrocycle framework (MMF): supramolecular nano-channel surfaces with shape sorting capability

Hollow nanostructures for the functional assembly of chemical groups with inner surface geometry and regulable stoichiometry enable steric design of interior reaction centers. Herein we report a metal-macrocycle framework (MMF) that forms single-crystalline nanochannels with five distinct enantiomeric pairs of guest binding pockets. During crystal-soaking experiments, the MMF crystals can encapsulate aromatic molecules with high site selectivity. First, constitutional isomers of dibromobenzene are captured and sorted into different binding pockets. Second, each of the optical isomers of (1R/1S)-1-(3-chlorophenyl)ethanol is included diastereoselectively into one of an enantiomeric pair of binding pockets. An advantage of this strategy is that the interior walls can be "repainted" via replacement of the trapped molecules with alternatives. Such guest uptake behaviors would allow highly regioselective or stereoselective reactions within the nanochannel.     

纳通道的物质传输特性及应用

近年来,随着材料科学、微纳加工技术和微纳尺度物质传输理论的发展,纳通道技术得到了越来越多的研究和关注。纳通道包括生物纳通道和人工纳通道,其孔径通常为1~100 nm。在这一尺度下,通道表面与通道内物质之间的作用概率大大增强,使得纳通道表现出许多与宏观体系不同的物质传输特性,例如通道表面电荷与通道内离子之间的静电作用产生了离子选择性,通道内电化学势的不对称分布产生了离子整流特性,物质传输过程中占据通道产生了阻塞脉冲特性等。纳通道中的这些物质传输特性在传感、分离、能源等领域具有广泛应用,例如通过对纳通道进行功能化修饰可以实现门控离子传输;利用亚纳米尺度的通道可以实现单分子传感;利用通道与传输物质之间的相互作用可以实现离子、分子、纳米粒子的分离;利用纳通道的离子选择性可以在通道内实现电荷分离,将不同形式的能量（如光、热、压力、盐差等）高效转化为电能。纳通道技术是化学、材料科学、纳米技术等多学科的交叉集合,在解决生物、环境、能源等基本问题方面具有良好的前景。该文综述了近10年来与纳通道物质传输理论以及纳通道技术应用相关的前沿研究,梳理了纳通道技术的发展过程,并对其在各个领域的应用进行了总结与展望。     

Creating anodic alumina nanochannel arrays with custom-made geometry

Porous anodic alumina oxide (AAO) is one of the most commonly used nanotemplates for growing arrays of nanoparticles, nanowires, nanocomposites, and nanoarchitectures because its pores, which are of a very uniform size, can grow longitudinally into arrays of self-aligned nanochannels with an extremely high aspect ratio. Furthermore, under specific combinations of anodization voltage and electrolyte, the lateral positions of nanochannels can self-organize into arrays of two-dimensional hexagonally close-packed lattices with domain sizes on the order of few tens of lattice units. The domain size can be greatly increased by prepatterning the Al surface with custom-designed nanoconcaves prior to the anodization process. The concaves guide the growth fronts of nanochannels and lead to the formation of an ideally long-range ordered lattice of nanochannel array. Such concaves have been fabricated by many methods, such as stamp imprinting, grating imprinting, and focused ion beam direct writing. In this review, we summarize the development of various methods to create AAO nanochannel arrays with custom-made geometry and discuss the mechanism responsible for the guiding process.     

Confinement Effect of Organic Nanotubes Toward Green Fluorescent Protein (GFP) Depending on the Inner Diameter Size

Transportation, release behavior, and stability of a green fluorescent protein (GFP, 3×4 nm) in self‐assembled organic nanotubes with three different inner diameters (10, 20, and 80 nm) have been studied in terms of novel nanocontainers. Selective immobilization of a fluorescent acceptor dye on the inner surface enabled us to not only visualize the transportation of GFP in the nanochannels but to also detect release of the encapsulated GFP to the bulk solution in real time, based on fluorescence resonance energy transfer (FRET). Obtained diffusion constants and release rates of GFP markedly decreased as the inner diameter of the nanotubes was decreased. An endo‐sensing procedure also clarified the dependence of the thermal and chemical stabilities of the GFP on the inner diameters. The GFP encapsulated in the 10 nm nanochannel showed strong resistance to heat and to a denaturant. On the other hand, the 20 nm nanochannel accelerated the denaturation of the encapsulated GFP compared with the rate of denaturation of the free GFP in bulk and the encapsulated GFP in the 80 nm nanochannels. The confinement effect based on rational fitting of the inner diameter to the size of GFP allowed us to store it stably and without denaturation under high temperatures and high denaturant concentrations.     

DNA tracking within a nanochannel: device fabrication and experiments

Fabrication of nanochannels is drawing considerable interest due to its broad applications in nanobiotechnology (e.g. biomolecular sensing and single DNA manipulation). Nanochannels offer distinct advantages in allowing a slower translocation and multiple sensing spots along the channel, both of which improve the read-out resolution. However, implementing electrodes inside the nanochannel has rarely been demonstrated to our knowledge. The device described in this work is a Si-Glass anodically bonded Lab-on-a-Chip (LOC) device of a few millimetres in size capable of performing DNA manipulation. The LOC device structure is based on two mainstream microchannels interconnected by nanochannels. DNA, once trapped within the nanochannel, has been tracked throughout the length of the channel and the data have been recorded and analysed.     

Construction and application of photoresponsive smart nanochannels

In living organisms, many biological processes are inextricably linked with light, such as the photosynthesis systems and rhodopsin. Hence, construction of light-sensitive biomimetic-nanochannels, which can realize the functions of cells and other membrane structures with high degree of spatial and temporal control, is particularly attractive and challenging. As a cornerstone of light-sensitive nanochannels, the photoresponsive materials are a big family and at their mature stage after several decades of development, which can provide different strategies to construct biomimetic photoresponsive nanochannels. In this review, we mainly summarize the construction and applications of photoresponsive nanochannels on the basis of various photoresponsive materials. The construction of photoresponsive nanochannels can be classified into four categories: photoresponsive inorganic nanochannels based on inorganic-compound-based photonic sensitive materials; photoresponsive organic nanochannels based on organic-compound-based photonic sensitive materials; photoresponsive polymers nanochannel based on photoresponsive polymers materials and potential photoresponsive nanochannels based on other photoresponsive materials. After introducing the construction of photoresponsive nanochannels, the review highlights some of the most recent applications of photoresponsive nanochannels in separation, energy conversion and storage, drug delivery and so on.     

纳米通道内表面浸润性对气泡的作用

运用分子动力学模拟方法研究了在质量力驱动下不同浸润性壁面纳米通道中气泡的分布及其运动状况, 提出了一种统计纳米通道中气泡运动速度的方法. 结果显示, 在亲水性壁面的纳米通道中, 气泡位于通道中间, 气泡的运动速度接近但小于通道中心流速, 在势能强度较大时, 壁面吸附的分子较多, 气泡也较大, 反之则气泡较小; 对超疏水性壁面, 气泡则位于固壁附近, 两个壁面形成对称的一对气泡, 气泡的运动速度接近但大于边缘速度. 流体总的流动速度随着流体粒子与壁面粒子作用的减弱而增大, 滑移速度则逐渐从负转变为正.     

Electrokinetic transport through nanochannels

This article presents a numerical study of the electrokinetic transport phenomena (electroosmosis and electrophoresis) in a three-dimensional nanochannel with a circular cross-section. Due to the nanometer dimensions, the Boltzmann distribution of the ions is not valid in the nanochannels. Therefore, the conventional theories of electrokinetic flow through the microchannels such as Poisson-Boltzmann equation and Helmholtz-Smoluchowski slip velocity approach are no longer applicable. In the current study, a set of coupled partial differential equations including Poisson-Nernst-Plank equation, Navier-Stokes, and continuity equations is solved to find the electric potential field, ionic concentration field, and the velocity field in the three-dimensional nanochannel. The effects of surface electric charge and the radius of nanochannel on the electric potential, liquid flow, and ionic transport are investigated. Unlike the microchannels, the electric potential field, ionic concentration field, and velocity field are strongly size-dependent in nanochannels. The electric potential gradient along the nanochannel also depends on the surface electric charge of the nanochannel. More counter ions than the coions are transported through the nanochannel. The ionic concentration enrichment at the entrance and the exit of the nanochannel is completely evident from the simulation results. The study also shows that the flow velocity in the nanochannel is higher when the surface electric charge is stronger or the radius of the nanochannel is larger.     

Detection of nonfluorescent molecules using differential interference contrast thermal lens microscope for extended nanochannel chromatography

An ultrasensitive absorbance detector, the differential interference contrast thermal lens microscope (DIC-TLM), was employed for a chromatography system using silica nanochannel. Recently, separation of ultrasmall volume sample has been strongly required for single-cell biological and chemical analysis. Previously, we have developed a chromatography system using nanochannels of ~100 nm scale (extended nanochannels) fabricated on a silica substrate. The extended nanochromatography realized highly efficient separation of samples <1 fL without packing materials. However, its detection method was limited to fluorescence method due to the small volume, and a new detector based on absorbance has been required. On the contrary, we have also developed DIC-TLM, a photothermal spectrometer based on absorption and thermal relaxation of sample for determination of concentration of nonfluorescent molecules in extended nanochannel. In this paper, we combined the extended nanochromatography and the DIC-TLM for separation and detection of nonfluorescent dyes. Particularly, basic performances of the DIC-TLM including quantitative performance and sensitivity were deliberated for injected samples of ~fL volume.     

Pressure-driven flow control system for nanofluidic chemical process

We developed a novel flow control system for a nanofluidic chemical process. Generally, flow control in nanochannels is difficult because of its high-pressure loss with very small volume flow rate. In our flow control method, liquid pressure in a microchannel connected to the nanochannels is regulated by utilizing a backpressure regulator. The flow control method was verified by using simple structured microchip, which included parallel nanochannels. We found that the observed flow rate was three times lower than the value expected from Hagen-Poiseuille's equation. That implied a size-dependent viscosity change in the nanochannels. Then, we demonstrated mixing of two different fluorescent solutions in a Y-shaped nanochannel and also a proton exchange reaction in the Y-shaped nanochannel. The flow control method will contribute to further integration of nanochemical systems.     

Understanding flow enhancement in graphene‐coated nanochannels

In this work, we investigate pressure‐driven water flows in graphene‐coated copper nanochannels through molecular dynamics simulations. It is found that the flow rate in bare copper nanochannel can be significantly enhanced by a factor of 45 when the nanochannel is coated with monolayer graphene. The enhancement factor for the flow rate reaches about 90 when the nanochannel is modified with 3 or more graphene layers. The dipole relaxation time and the hydrogen bond lifetime of interfacial water molecules show that the graphene coating promotes the mobility of water molecules at the interface. The distribution of the potential of mean force and the free energy barriers also confirm that graphene coating reduces the flow resistance and 3 layers of graphene can fully screen the surface effects. The results in this work provide important information for the design of graphene‐based nanofluidic systems for flow enhancement.     

Gold Nanoparticles Confined in Vertically Aligned Silica Nanochannels and Their Electrocatalytic Activity Toward Ascorbic Acid

A facile method of confining gold nanoparticles (AuNPs) in silica nanochannels aligned perpendicularly to an underlying electrode surface is reported. The nanochannel surface carrying a layer of (3‐aminopropyl)triethoxy silane (APTS) displays a strong electrostatic interaction with AuCl₄^?, eventually resulting in the confinement of AuNPs inside the nanochannels after chemical reduction. As‐prepared AuNPs in APTS‐modified mesoporous silica film (APTS‐MSF) are highly dispersed with a narrow size distribution. Furthermore, these AuNPs are free of protecting ligands and exhibit a good electrochemical catalytic activity toward the oxidation of ascorbic acid.     

The influence of energetic surface heterogeneity on proton desorption during capillary filling of silica nanochannels

We applied the surface complexation model to describe the deprotonation of silica nanochannel walls as a function of pH and ionic strength of filling solution. We took into account energetic heterogeneity of silanol groups. We found that more heterogeneous walls of silica nanochannel will be more charged and can interact more strongly with ionic solutes. The modeling of nanochannels coated with 3-cyanopropydimethylchlorosilane is uncertain because charging mechanism of coated silica should take into account increased autolysis of interfacial water.     

Biosensing with Functionalized Single Asymmetric Polymer Nanochannels

In this work, we describe the direct covalent attachment of protein recognition elements (biotin) with the carboxyl groups present on the walls of polyimide nanochannels. Subsequently, these biotinylated channels were used for the bio‐specific sensing of protein analytes. Moreover, surface charge of these asymmetric nanochannels was reversed from negative to positive via the conversion of carboxyl groups into terminated amino groups. The negatively charge (carboxylated) and positively charged (aminated) channels were further used for the electrochemical sensing of bovine serum albumin (BSA, pI = 4.7). These biorecognition events were assessed from the changes in the ionic current flowing through the nanochannel.

     

Selective sensing and transport in bionic nanochannel based on macrocyclic host-guest chemistry

Imitating the signal transduction and transmembrane transport co ntrolled by biological channels in the cell membra ne,artificial nanochannels with a similar capability of sensing and transport are constructed as bionic nanochannels.To accomplish selective sensing and transport of biological analyte(as "guest"),the bionic nanochannels are modified with the artificial receptor(as "host"),Based on selective recognition between host and guest,bionic nanochannels translate the stimulus of the guest to electrochemical signal as sensors,and further regulate the transmission of guest as transporters.Howeve r,throughout all kinds of guests,the selective sensing and transpo rt of ions and chiral molecules is a challenging problem.And throughout all hosts of ions and chiral molecules,the macrocyclic hosts with multisite of recognition show better selectivity,such as crown ethers,cyclodextrins,calixarenes,and pillararenes.In this article,we highlight recent advances in the macrocyclic host-based nanochannels for the selective sensing and transport of ionic and chiral guests,summarize the similarities and differences of different kinds of macrocyclic host-based nanochannels,and expect the research direction and application prospect.     

Diffusioosmotic flows in slit nanochannels

Diffusioosmotic flows of electrolyte solutions in slit nanochannels with homogeneous surface charges induced by electrolyte concentration gradients in the absence of externally applied pressure gradients and potential differences are investigated theoretically. A continuum mathematical model consisting of the strongly coupled Nernst-Planck equations for the ionic species' concentrations, the Poisson equation for the electric potential in the electrolyte solution, and the Navier-Stokes equations for the flow field is numerically solved simultaneously. The induced diffusioosmotic flow through the nanochannel is computed as functions of the externally imposed concentration gradient, the concentration of the electrolyte solution, and the surface charge density along the walls of the nanochannel. With the externally applied electrolyte concentration gradient, a strongly spatially dependent electric field and pressure gradient are induced within the nanochannel that, in turn, generate a spatially dependent diffusioosmotic flow. The diffusioosmotic flow is opposite to the applied concentration gradient for a relatively low bulk electrolyte concentration. However, the electrolyte solution flows from one end of the nanochannel with a higher electrolyte concentration to the other end with a lower electrolyte concentration when the bulk electrolyte concentration is relatively high. There is an optimal concentration gradient under which the flow rate attains the maximum. The induced flow is enhanced with the increase in the fixed surface charge along the wall of the nanochannel for a relatively low bulk electrolyte concentration.     

A simple polysilsesquioxane sealing of nanofluidic channels below 10 nm at room temperature

We present a simple sealing method to fabricate nanofluidic channels, where plasma treated polysilsesquioxane (PSQ) thin film on a rigid support is used to bond to a hydrophilic glass surface permanently at room temperature. This method shows precise dimension control below 10 nm with easy experimental setup. Using this method, one dimensional confined shallow nanochannels with a depth as small as 8 nm and an aspect ratio of <4 x 10(-5), two dimensional confined nanochannel arrays, and integrated nano/microchannel devices with a micro-to-nano interface have been demonstrated. Smooth transfer of DNA fragments from microchannel to nanochannel through the interface area was observed.