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An asymmetrical architecture is developed to discriminate monosaccharide enantiomers based on enzyme-like cascade reactions in homochiral CuMOF pockets. The increased enzyme-like activity under LSPR excitation enhanced the identification performance.

Harvesting the low-grade (

Biological ion pumps with two separate gates can actively transport ions against the concentration gradient. Developing an artificial nanofluidic device with multiple responsive sites is of great importance to improve its controllability over ion transport to further explore its logic function and mimic the biological process. Here, we propose an electrochemical polymerization method to fabricate electrochemically switchable double-gate nanofluidic devices. The ion transport of the double-gate nanofluidic device can be in situ and reversibly switched among four different states. The logic function of this nanofluidic device is systematically investigated by assuming the gate state as the input and the transmembrane ionic conductance as the output. A biomimetic electrochemical ion pump is then established by alternately applying two different specific logic combinations, realizing an active ion transport under a concentration gradient. This work would inspire further studies to construct complex logical networks and explore bioinspired ion pump systems.

Ion transport in nanochannels of a size comparable to that of hydrated ions exhibits unique properties due to the synergistic effect of various forces. Here, we design a nanochannel/ion channel composite (NIC) membrane that shows a high ion current rectification (ICR) ratio in different electrolytes. Experimental and theoretical results demonstrate that the synergistic effect of electrostatic interaction and ionic dehydration plays an important role in regulating the ICR behavior of the NIC membrane. We find that electrostatic attraction between ions and the channel surface in the ultraconfined space increases the probability of ionic dehydarion, resulting in different dehydration energy costs for different ions. This further alters the driving force for ion transport and thus regulates ICR of the NIC membrane. This work provides fundamental knowledge of ion transport in ion channels, which aids in the understanding of the function of biological systems and the design of high-performance nanochannel devices.

As an intriguing and intrinsic feature of life, chirality is highly associated with many significant biological processes. Simultaneous recognition and quantification of enantiomers remains a major challenge. Here, a sensitive enantiomer identification device is developed on TiO

Inspired by electronic transistors, electric field gating has been adopted to manipulate ionic currents of smart nanofluidic devices. Here, we report a PNP nanofluidic bipolar junction transistor (nBJT) consisting of one polyaniline (PANI) layer sandwiched between two polyethylene terephthalate (PET) nanoporous membranes. The PNP nBJT exhibits three different responses of currents (quasi-linear, rectification, and sigmoid) due to the counterbalance between surface charge distribution and base voltage applied in the nanofluidic channels; thus, they can be switched by base voltage. Four operating modes (cutoff, active, saturation, and breakdown mode) occur in the collector response currents. Under optimal conditions, the PNP nBJT exhibits an average current gain of up to 95 in 100 mM KCl solution at a low base voltage of 0.2 V. The present nBJT is promising for fabrication of nanofluidic devices with logical-control functions for analysis of single molecules.

High ion selectivity and permeability, as two contradictory aspects for the membrane design, highly hamper the development of osmotic energy harvesting technologies. Metal-organic frameworks (MOFs) with ultra-small and high-density pores and functional surface groups show great promise in tackling these problems. Here, we propose a facile and mild cathodic deposition method to directly prepare crack-free porphyrin MOF membranes on a porous anodic aluminum oxide for osmotic energy harvesting. The abundant carboxyl groups of the functionalized porphyrin ligands together with the nanoporous structure endows the MOF membrane with high cation selectivity and ion permeability, thus a large output power density of 6.26 W m

Ion transport in bionanopores is closely related to biological processes and can be regulated by various external stimulations. Multivalent ion as one of the stimulators shows a great ability in tu...

Micro-/nanofluidics has received considerable attention over the past two decades, which allows efficient biomolecule trapping and preconcentration due to ion concentration polarization (ICP) within nanostructures. The rich scientific content related to ICP has been widely exploited in different applications including protein concentration, biomolecules sensing and detection, cell analysis, and water purification. Compared to pure microfluidic devices, micro-/nanofluidic devices show a highly efficient sample enrichment capacity and nonlinear electrokinetic flow feature. These two unique characterizations make the micro-/nanofluidic systems promising in high-performance bioanalysis. This review provides a comprehensive description of the ICP phenomenon and its applications in bioanalysis. Perspectives are also provided for future developments and directions of this research field.

Membrane-based ion separation is environmentally friendly, energy-efficient, and easy to integrate, being widely used in water desalination and purification systems. With the existing separation technologies, it is yet difficult to achieve real time, in situ, and reversible control of the separation process. Here, we design and fabricate a Prussian blue (PB) coordination polymer based membrane with uniform and electrochemically size-tunable subnanopores. The ion separation can be significantly and reversibly modulated through the electrochemical conversion between PB and Prussian white (PW). The permeation rates of small hydrated metal ions (Cs+ and K+) obviously increase upon switching from PB to PW, while the permeation rates of large hydrated metal ions (Li+, Na+, Mg2+, and La3+) remain constant. The membrane selectivity of small hydrated ions to large hydrated ions can be increased by more than 2 times during the electrochemical switch, which could be assigned to the slightly larger crystal size (e.g., pore window size) of PW than PB. The present approach provides a new strategy for constructing tunable seawater desalination and ion extraction systems.

The unique phenomena of ion selectivity and ion current rectification (ICR) in nanofluidics have been widely used to construct bioinspired channels and organs, sensors, and power generators. However, the excellent performance of a single nanochannel does not show a linear increase when it is scaled up into multiple nanochannels in tandem and parallel structure, and in some cases, it even shows a reverse trend. Understanding of this scaling-up inconsistency in nanofluidics is essential to the design of functional devices. Here, we provide a method for investigating the ion transport properties in multiple nanochannels in tandem and parallel connections. We find that interfacial resistance caused by ion concentration polarization (ICP) in tandem and parallel nanochannels has a significant impact on ICR, showing a nonlinear scaling-up feature with the tandem number and a decreased trend with the parallel number, which is not expected in electronic devices. We further verify that it is feasible to regulate ion transport in tandem and parallel nanochannels by adding gap distances between nanochannels in tandem and parallel structures to decouple the ICP region between nanochannels. This study provides fundamental insights into the ion transport properties in nanofluidic circuits, which hold promise for the design of high-performance nanofluidic devices in the fields of separation, energy, and sensors.

For study of the photocatalytic reaction kinetics in a confined microsystem, a photocatalysis microreactor integrated on a microfluidic device has been fabricated using an on-line UV/vis detector. The performance of the photocatalysis microreactor is evaluated by the photocatalytic degradation of Rhodamine B chosen as model target by using commercial titanium dioxide (Degussa P25, TiO2) nanoparticles as a photocatalyst. Results show that the photocatalytic reaction occurs via the Langmuir-Hinshelwood mechanism and the photocatalysis kinetics in the confined microsystem (r = 0.359 min−1) is about 10 times larger than that in macrosystem (r = 0.033 min−1). In addition, the photocatalysis activity of the immobilized TiO2 nanoparticles in the microreactor exhibits good stability under flowing conditions. The present microchip device offers an interesting platform for screening of photocatalysts and exploration of photocatalysis mechanisms and kinetics.

Noble metal nanoparticles are promising catalysts in electrochemical reactions, while understanding the relationship between the structure and reactivity of the particles is important to achieve higher efficiency of electrocatalysis, and promote the development of single-molecule electrochemistry. Electrogenerated chemiluminescence (ECL) was employed to image the catalytic oxidation of luminophore at single Au, Pt, and Au-Pt Janus nanoparticles. Compared to the monometal nanoparticles, the Janus particle structure exhibited enhanced ECL intensity and stability, indicating better catalytic efficiency. On the basis of the experimental results and digital simulation, it was concluded that a concentration difference arose at the asymmetric bimetallic interface according to different heterogeneous electron-transfer rate constants at Au and Pt. The fluid slip around the Janus particle enhanced local redox reactions and protected the particle surface from passivation.

Fruit ripening is a progress involving many physiological changes regulated by various plant hormones such as indole-3-acetic acid (IAA) and salicylic acid (SA). The levels of these hormones in fruit with the spatial-temporal resolution can provide detailed information for the study and evaluation of the fruit ripening. Herein paper-based analytical devices and the microsampling technique were coupled for the analysis of IAA and SA in different locations of the tomato fruit during ripening. Because of its excellent electric conductivity, the ITO glass was used as the substrate of the disposable working electrodes and modified with conductive carbon cement. The ITO modified electrodes in the paper-based analytical devices were utilized for analysis of IAA and SA in tiny tomato samples obtained with the technique of microsampling. Our results showed that the amounts of IAA and SA in the locular tissue of tomato fruit decreased via time in the process of ripening. More importantly, the spatial profiling of IAA and SA in immature and mature tomatoes could be directly differentiated at the molecular level. This study suggested that low-cost paper-based electroanalytical devices could become an effective platform for rapid evaluation of the fruit ripening.

Electrochemical biosensors based on enzymatic reaction have been applied to a wide range of fields. As the trend continues to grow, these biosensors are approaching the limit imposed by physics and chemistry. To further improve the performance of biosensors, the interplay of mass transport and enzymatic reaction kinetics, especially in enzyme cascade systems, should be considered in the design of biosensors. Herein, we propose a simple approach to studying the influence of mass transport and enzyme molecule motion on the kinetics of enzyme cascade reactions. β-Galactosidase (β-Gal) and glucose oxidase (GOx) of the enzyme cascade reaction are precisely immobilized onto the disk and ring electrodes, respectively, of a rotating ring-disk electrode (RRDE) via covalent attachment. At a low rotating speed (

In the work, we showed that the use of nanoemitters (tip dimension1 μm, typically ∼100 nm) could dramatically reduce the nonspecific metal adduction to peptide or protein ions as well as improve the matrix tolerance of electrospray ionization mass spectrometry (ESI-MS). The proton-enriched smaller initial droplets are supposed to have played a significant role in suppressing the formation of metal adduct ions in nanoemitters. The proton-enrichment effect in the nanoemitters is related to both the exclusion-enrichment effect (EEE) and the ion concentration polarization effect (ICP effect), which permit the molecular ions to be regulated to protonated ones. Smaller initial charged droplets generated from nanoemitters need less fission steps to release the gas-phase ions; thus, the enrichment effect of salt was not as significant as that of microemitters (tip dimension1 μm), resulting in the disappearing of salt cluster peaks in high mass-to-charge (m/z) region. The use of nanoemitters demonstrates a novel method for tuning the distribution of the metal-adducted ions to be in a controlled manner. This method is also characterized by ease of use and high efficiency in eliminating the formation of adduct ions, and no pretreatment such as desalting is needed even in the presence of salt at millimole concentration.

Room temperature ionic liquids are salts which are molten at or around room temperature without any added solvent or solution. In bulk they exhibit glass like dependence of conductivity with temperature as well as coupling of structural and transport properties. Interfaces of ionic liquids have been found to induce structural changes with evidence of long range structural ordering on solid-liquid interfaces spanning length scales of 10-100 nm. Our aim is to characterize the influence of confinement on the structural properties of ionic liquids. We present the first conductivity measurements on ionic liquids of the imidazolium type in single conical glass nanopores with confinements as low as tens of nanometers. We probe glassy dynamics of ionic liquids in a large range of temperatures (-20 to 70 degrees C) and nanopore opening sizes (20-600 nm) in silica glass nanocapillaries. Our results indicate no long range freezing effects due to confinement in nanopores with diameters as low as 20 nm. The studied ionic liquids are found to behave as glass like liquids across the whole accessible confinement size and temperature range.

Early diagnosis and therapy of cancer metastasis are of great importance for disease outcome. Circulating tumor cells (CTCs) offer the ability for noninvasive tumor profiling in real time. However, simply capturing and counting tumor cells are inadequate to provide valuable information about tumor. Efficiently releasing the captured cells is necessary for the downstream characterization. Herein, we describe a mild electrochemical strategy to effectively isolate CTCs from the bloodstream and rapidly release the captured cells in 2 min for downstream molecular characterization, as realized on a conductive poly(aminophenylboronic acid) derivatized electrode. The boronic ester linkage between dopamine (DA) and boronic acids-functionalized electrode is stable, and only upon the application of a weak potential perturbation does the boronic ester dissociate and release cells without compromising cell viability. This platform is reusable after acid treatment and has the potential to be the next-generation platform for cell capture and release, realizing the clinical value of CTCs as biomarkers.

The spatial positioning of enzymes and mass transport play crucial roles in the functionality and efficiency of enzyme cascade reactions. To fully understand the mass transport regulating kinetics of enzyme cascade reactions, we investigated the contribution of convective and diffusive transports to a cascade reaction of β-galactosidase (β-Gal)/glucose oxidase (GOx) confined in a microchannel. β-Gal and GOx are assembled on two separated gold films patterned in a polydimethylsiloxane (PDMS) microchannel with a controllable distance from 50 to 100 μm. Experimental results demonstrated that the reaction yield increases with decreasing distance between two enzymes and increasing substrate flow rate. Together with the simulation results, we extracted individual reaction kinetics of the enzyme cascade reaction and found that the reaction rate catalyzed by β-Gal occurred much faster than by GOx, and thus, the β-Gal catalytic reaction showed diffusion controll, whereas the GOx catalytic reaction showed kinetic controll. Since the decrease in the enzymes distance shortens the transport length of intermediate glucose to GOx, the amount of glucose reaching GOx will be increased in the unit time, and in turn, the enzyme cascade reaction yield will be increased with decreasing the gap distance. This phenomenon is similar to the intermediates pool of tricarboxylic acid (TCA) cycle in the metabolic system. This study promotes the understanding of the metabolic/signal transduction processes and active transport in biological systems and promises to design high performance biosensors and biofuel cells systems.

Numerical simulation can provide valuable insights for complex microfluidic phenomena coupling mixing and diffusion processes. Herein, a novel finite element model (FEM) has been established to extract chemical reaction kinetics in a microfluidic flow injection analysis (micro-FIA) system using high throughput sample introduction. To reduce the computation burden, the finite element mesh generation is performed with different scales based on the different geometric sizes of micro-FIA. In order to study the contribution of chemical reaction kinetics under non-equilibrium condition, a pseudo-first-order chemical kinetics equation is adopted in the numerical simulations. The effect of reactants diffusion on reaction products is evaluated, and the results demonstrate that the Taylor dispersion plays a determining role in the micro-FIA system. In addition, the effects of flow velocity and injection volume on the reaction product are also simulated. The simulated results agree well with the ones from experiments. Although gravity driven flow is used to the numerical model in the present study, the FEM model also can be applied into the systems with other driving forces such as pressure. Therefore, the established FEM model will facilitate the understanding of reaction mechanism in micro-FIA systems and help us to optimize the manifold of micro-FIA systems.

A new ionic current rectification device responsive to a broad range of pH stimuli has been fabricated using porous anodic alumina membrane with tailor-made branching nanochannel array. The asymmetric geometry is achieved by changing oxidation voltage using a simple two-step anodization process. Due to the protonation/deprotonation of the intrinsic hydroxyl groups upon solution pH variation, the nanochannels array-based device is able to regulate ionic current rectification properties. The ion rectification ratio of the device is mainly determined by the branching size and surface charges, which is also confirmed by theoretical simulations. In addition, theoretical simulations show that the slight difference in ion rectification ratio for the nanochannel devices with different branching numbers is due to the propagation of concentration polarization. Three dimensional simulations clearly show the nonuniform concentration profiles in stem nanochannel near the junction interface due to the presence of branching nanochannels. The present ionic device is promising for biosensing, molecular transport and separation, and drug delivery in confined environments.

The sensitive identification of single nucleotide polymorphisms becomes increasingly important for disease diagnosis, prevention, and practical applicability of pharmacogenomics. Herein, we propose a simple, highly selective, label-free single nucleotide polymorphisms (SNPs) sensing device by electrochemically monitoring the diffusion flux of ferricyanide probe across probe DNA/morpholino duplex functionalized nanochannels of porous anodic alumina. When perfectly matched or mismatched target DNA flows through the nanochannels modified with probe DNA/morpholino duplex, it competes for the probe DNA from morpholino, resulting in a change of the surface charges. Thus, the diffusion flux of negatively charged electroactive probe ferricyanide is modulated since it is sensitive to the surface charge due to the electrostatic interactions in electric double layer-merged nanochannels. Monitoring of the change in diffusion flux of probe enables us to detect not only a single base or two base mismatched sequence but also the specific location of the mismatched base. As is demonstrated, SNPs in the PML/RARα fusion gene, known as a biomarker of acute promyelocytic leukemia (APL), have been successfully detected.

For study of the photocatalytic reaction kinetics in a confined microsystem, a photocatalysis microreactor integrated on a microfluidic device has been fabricated using an on-line UV/vis detector. The performance of the photocatalysis microreactor is evaluated by the photocatalytic degradation of Rhodamine B chosen as model target by using commercial titanium dioxide (Degussa P25, TiO

The effective capture and release of circulating tumor cells (CTCs) is of significant importance in cancer prognose and treatment. Here we report a highly efficient method to capture and release human leukemic lymphoblasts (CCRF-CEM) using aptamers modified gold nanowire arrays (AuNWs). The gold nanowires, showing tunable morphologies from relatively random pillar deposit to relatively uniform arrays, were fabricated by electrochemical deposition using anodic aluminum oxide (AAO) as template. Upon simply being modified with aptamers by Au–S chemistry, the AuNWs exhibit higher specificity to target cells. Also compared to flat gold substrate, the AuNWs with nanostructure can capture target cells with much higher capture yield. Moreover, the captured CCRF-CEM cells can be released from AuNWs efficiently with little damage through an electrochemical desorption process. We predict that our strategy has great potential in providing a simple and economical platform for CTCs isolation, cancer diagnosis, and therapy.

A microelectrode array has been applied for single cell analysis with relatively high throughput; however, the cells were typically cultured on the microelectrodes under cell-size microwell traps leading to the difficulty in the functionalization of an electrode surface for higher detection sensitivity. Here, nanoring electrodes embedded under the microwell traps were fabricated to achieve the isolation of the electrode surface and the cell support, and thus, the electrode surface can be modified to obtain enhanced electrochemical sensitivity for single cell analysis. Moreover, the nanometer-sized electrode permitted a faster diffusion of analyte to the surface for additional improvement in the sensitivity, which was evidenced by the electrochemical characterization and the simulation. To demonstrate the concept of the functionalized nanoring electrode for single cell analysis, the electrode surface was deposited with prussian blue to detect intracellular hydrogen peroxide at a single cell. Hundreds of picoamperes were observed on our functionalized nanoring electrode exhibiting the enhanced electrochemical sensitivity. The success in the achievement of a functionalized nanoring electrode will benefit the development of high throughput single cell electrochemical analysis.

Porous anodic alumina (PAA) film is composed of highly ordered and controllable structures, and their extensive application requires the understanding of their growing mechanism. Herein, we present a localized oxidation model to unravel the phenomena of PAA growth, showing that random processes converge into an ordered formation due to the unique characteristics of ion transport confinement in alumina. The anodizing voltage shows a quadratic relationship with barrier layer depth. In addition, we predict the furcate conditions of PAA and the voltage threshold to produce a PAA by our model.

Previously, our group has utilized the luminol electrochemiluminescence to analyze the active cholesterol at the plasma membrane in single cells by the exposure of one cell to a photomultiplier tube (PMT) through a pinhole. In this paper, fast analysis of active cholesterol at the plasma membrane in single cells was achieved by a multimicroelectrode array without the pinhole. Single cells were directly located on the microelectrodes using cell-sized microwell traps. A cycle of voltage was applied on the microelectrodes sequentially to induce a peak of luminescence from each microelectrode for the serial measurement of active membrane cholesterol. A minimal time of 1.60 s was determined for the analysis of one cell. The simulation and the experimental data exhibited a semisteady-state distribution of hydrogen peroxide on the microelectrode after the reaction of cholesterol oxidase with the membrane cholesterol, which supported the relative accuracy of the serial analysis. An eight-microelectrode array was demonstrated to analyze eight single cells in 22 s serially, including the channel switching time. The results from 64 single cells either activated by low ion strength buffer or the inhibition of intracellular acyl-coA/cholesterol acyltransferase (ACAT) revealed that most of the cells analyzed had the similar active membrane cholesterol, while few cells had more active cholesterol resulting in the cellular heterogeneity. The fast single-cell analysis platform developed will be potentially useful for the analysis of more molecules in single cells using proper oxidases.

A new ionic current rectification device responsive to a broad range of pH stimuli is established using highly ordered nanochannels of porous anodic alumina membrane with abrupt surface charge discontinuity. The asymmetric surface charge distribution is achieved by patterning the nanochannels with surface amine functional groups at designed positions using a two-step anodization process. Due to the protonation/deprotonation of the patterned amine and the remaining intrinsic hydroxyl groups upon solution pH variation, the nanochannel-array-based device is able to regulate ion transport selectivity and has ionic current rectification properties. The rectification ratio of the device is mainly determined by the nanochannel size, and the rectification ratio is less sensitive to the patterned length of the amine groups when the nanochannels size is defined. Thus, the isoelectric point of nanochannels can be easily estimated to be the pH value with a unit rectification ratio. The present ionic device is promising for biosensing, molecular transport and separation, and drug delivery in confined environments.

In biological metabolism, a given metabolic process usually occurs via a group of enzymes working together in sequential pathways. To explore the metabolism mechanism requires the understanding of the multienzyme coupled catalysis systems. In this paper, an approach has been proposed to study the kinetics of a two-enzyme coupled reaction using SECM combining numerical simulations. Acetylcholine esterase and choline oxidase are immobilized on cysteamine self-assembled monolayers on tip and substrate gold electrodes of SECM via electrostatic interactions, respectively. The reaction kinetics of this two-enzyme coupled system upon various separation distance precisely regulated by SECM are measured. An overall apparent Michaelis-Menten constant of this enzyme cascade is thus measured as 2.97 mM at an optimal tip-substrate gap distance of 18 μm. Then, a kinetic model of this enzyme cascade is established for evaluating the kinetic parameters of individual enzyme by using the finite element method. The simulated results demonstrate the choline oxidase catalytic reaction is the rate determining step of this enzyme cascade. The Michaelis-Menten constant of acetylcholine esterase is evaluated as 1.8 mM. This study offers a promising approach to exploring mechanism of other two-enzyme coupled reactions in biological system and would promote the development of biosensors and enzyme-based logic systems.

A novel method for transporting micro-fluids in vertical direction is presented, by which a paper-based micro-fluidic device can implement pretreatment operations of samples. Interdigital transducers (IDTs) and reflectors were fabricated on a 128° yx-LiNbO 3 substrate using micro-electric technique. A paper-based micro-fluidic device was placed on PDMS blocks, which were mounted on a piezoelectric substrate. The space between the paper-based micro-fluidic device and the piezoelectric substrate is 2 mm. Two surface acoustic waves (SAWs) in opposite transportation directions were excited when an amplified RF signal was applied to the IDTs. And then, the micro-fluid to be analyzed was transported vertically to the paper substrate by the SAWs. The transportation experiments were carried out using red dye solution micro-fluids with different volumes. The results indicated that the volume of the micro-fluid and the RF signal power can affect the successful transportation of the micro-fluid from the piezoelectric substrate to the paper substrate. The detection of NO 2 − was also examined using the presented method.

We report a controllable method to fabricate silica colloidal crystals at defined position in microchannel of microuidic devices using simple surface modification. The formed PCs (photonic crystals) in microfluidic channels were stabilized by chemical cross-linking of Si-O-Si bond between neighboring silica beads. The voids among colloids in PCs integrated on microfluidic devices form interconnected nanoporous networks, which show special electroosmotic properties. Due to the "surface-charge induced ion depletion effect" mechanism, FITC-labeled proteins can be efficiently and selectively concentrated in the anodic boundary of the ion depletion zone. Using this device, about 10(3) - to 10(5)-fold protein concentration was achieved within 10 min. The present simple on chip protein concentration device could be a potential sample preparation component in microfluidic systems for practical biochemical assays.

Diffusion is the principal means of passive transport whereby ions or molecules driven by thermal motion move along their concentration gradients. This spontaneous process is widespread in nature. For example, as the main form of transport for vital materials through cell membranes, diffusion plays a fundamental role in living cells. Recently, self-supporting membranes that contain single or arrays of nanochannels are attracting increasing attention in nanotechnology, chemistry, physics, and biology. Inspired by biological membrane channel systems, most notably the a-hemolysin channel, artificial analogues of such nanoscopically sized pores have been developed for potential application in controlled growth of nanostructures, nanofiltration devices, bioseparation, and biosensing. Compared to biologically based nanochannels, artificial inorganic nanochannels have potential advantages of being less fragile, more stable, easily tailored, and flexible with regard to surface modification. Anodization of aluminum under appropriate electrochemical conditions yields extended membranes containing self-assembled, uniform, parallel pores with diameters of a few tens to a few hundreds of nanometers, high pore density, and well-defined morphology. Such porous anodic alumina (PAA) membranes could find applications in chemical and biological separations as well as for analytical purposes. Motion of molecules across these charged membranes is the basis of numerous systems of technological and biological interest. Detailed knowledge of such mass-transport behavior is therefore crucial for understanding and optimizing prospective device structures. Although many application models have been successfully established on the basis of the widely studied migration mechanism of ions or charged biomolecules in nanochannels, little is known about the motion of electrically neutral molecules on this size scale. Herein we show a distinct diffusion phenomenon of electrically neutral molecules in charged alumina nanochannels. Mass transfer across a porous membrane is governed by the Nernst–Planck equation. For a one-dimensional system, the mass transfer J along the x axis can be written as Equation (1) where D, C, and z are the diffusion coefficient

In this article, an approach of finite element method has been introduced to predict the distribution of potential and current on electrode surfaces. In this method, the bulk of electrolyte solution and the main body of solid electrodes are modeled to be normal conductive media; while the surface of the electrode, whose current–potential ( I – V ) curve satisfies experimental data, is modeled to be special nonlinear boundary conditions. This modeling approach for electrochemistry system is successfully verified by experimental data, and would contribute to a better understanding of the distribution of electrical potential and current at electrode surfaces in practical systems with high voltage coupling effect.

In this paper, a micro/nanofluidic preconcentration device integrated with an electrochemical detector has been used to study the enrichment of enzymes and homogeneous enzyme reaction kinetics. The enzymes are first concentrated in front of a nanochannel via an exclusion-enrichment effect (EEE) mechanism of the nanochannel integrated in a microfluidics device. If a substrate is electrokinetically transported to the concentrated enzymes, homogeneous enzymatic reaction occurs. The enzymatic reaction product can penetrate through the nanochannel to be detected electrochemically. In this device, the enriched enzymes can be well retained and repeatedly used, thus, the enzymatic reaction occurs in a continuous-flow mode. For demonstration, Glucose oxidase (GOx) was chosen as the model enzyme to study the influence of enzyme concentration on its reaction kinetics. The different concentration of GOx in front of the nanochannel was simply achieved by using different enrichment time. When substrate glucose was introduced electrokinetically, a rapid electrochemical steady-state response could be obtained. It was found that the electrochemical response to a constant glucose concentration increased with the increase of enzyme enrichment time, which is expected for homogeneous enzymatic reactions. Under proper conditions, the electrochemical responds linearly to the glucose concentration ranging from 0 to 15 mM, and the Michaelis constants (K(m)) are relatively low, which indicates a more efficient complex formation between enzyme and substrate. These results suggest that the present micro/nanofluidics device is promising for the study of enzymatic reaction kinetics and other bioassays such as cell assays, drug discovery, and clinical diagnosis.

The hysteresis dynamics of a multi-domain Potts lattice with non-zero domain wall width is simulated using kinetic Monte-Carlo method. The remanence enhancement effect is investigated, taking into account polarization relaxation in domain walls. Significant enhancement of the remanence and weakening of the coercivity with increasing domain walls are revealed. The hysteresis area is conserved against variation of domain size and wall width, which predicts that no excess energy is required for the polar relaxation in domain walls, thus the remanence enhancement. The theoretically predicted scaling relation on the remanence enhancement is confirmed with the present simulation.

Zinc oxide ceramics doped with 5–15at%-Li are sintered and completely c-oriented 5–15at%Li-doped ZnO thin films are fabricated on fused silica using PLD technique. The dielectric and ferroelectric properties of the Li-doped ZnO bulk samples are investigated. A broad peak in the dielectric spectrum is probed, indicating a ferroelectric transition. The thin films doped with 7.5at% and 10at%-Li show clean ferroelectric hysteresis. The transmittance spectrum over wavelength range 300 to 1400 nra was measured. All the spectra of the different dopant percentage samples produce the same absorption edge, which indicates that Li-doping has negligible influence on the band gap of ZnO.

Polycrystalline ${\mathrm{La}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3\ensuremath{-}\ensuremath{\delta}}$ thin films deposited on quartz wafers at 680 \ifmmode^\circ\else\textdegree\fi{}C and various oxygen pressures P by pulsed laser deposition are prepared. The effects of oxygen nonstoichiometry on the microstructural, electrotransport and low-field magnetotransport property of the thin films are investigated in details. A structural distortion from the stoichiometric lattice is identified for the samples deposited at $Pl0.1\mathrm{mbar}.$ It is verified that the thin-film conductivity over the Curie point follows variable-range hopping. The carrier density at the Fermi surface falls and the metal-insulating transition shifts toward low temperature with decreasing P, with a jump at $P=0.1\mathrm{mbar}.$ Enhanced low-field magnetoresistance at low temperature is achieved for $Pg0.1\mathrm{mbar}.$ Oxygen overdeficiency at $Pl~0.1\mathrm{mbar}$ essentially prohibits the spin reordering. The temperature dependence of the electro- and magnetotransport properties is explained by the two-channel model where the insulating channels and metallic ones coexist in parallel.

Propagation of the plume formed by pulsed laser ablation of PbTiO3 in an ambient of oxygen and argon was studied by using a CCD camera. Two optical filters with different transmittance bands were used to distinguish the atomic processes in the plume. The results show that, if a strong shock wave is formed, the propagation of the plume formed in pulsed laser deposition in oxygen ambient can be classified into four successive regions from the target to the substrate: (1) the plasma region nearby the target surface; (2) the shock wave forming region in which the interactions between ablated species and ambient oxygen are not chemically reactive; (3) the shock wave propagation region in which the excitations, dissociations, and ionizations, as well as gas-phase chemical reactions between ablated species and ambient oxygen occur; and (4) sound wave region.

A Monte-Carlo algorithm for dynamic hysteresis simulation in Q-state Potts spin lattice is developed and a detailed investigation on Q-dependence of the hysteresis is performed. It reveals that a significant dependence of the hysteresis pattern on the number of the spin states in lattice is identified and the decayed oscillation of both remanence and coercivity with Q is established. This dependence is explained using a simple geometric model. In addition, a series of parameters characterizing the hysteresis pattern and domain boundaries, as a function of Q and external field, are simulated and discussed.

On SiO 2 /Si substrate (Si wafer with thermally oxidized SiO 2 coating), only polycrystalline LiNbO 3 thin films were normally obtained. In this work, we found that an ultrathin layer of predeposited Al 2 O 3 layer on SiO 2 /Si has greatly mediated the growth pattern of the subsequently deposited LiNbO 3 films. As a result, highly or completely (001) textured LiNbO 3 films were achieved depending on the substrate temperature and the thickness of Al 2 O 3 as well. The textured growth phenomenon is discussed in terms of surface energy relation.

A low electrical field applied during pulsed laser deposition of ferroelectric thin films or multilayers has a significant influence on the texture of the ferroelectric films and layers, leading to an oriented growth with the poling direction of the films parallel to the applied electrical field. Highly (001) oriented LiNbO3 films have been prepared in a bias electrical field less than 10V/cm on different kinds of substrates. With the help of this method a series of (001) LiNbO3 / amorphous A12O3 multilayers with modulation period of several nm to several hundred nm were prepared sucessfully. In these “acoustic superlattices” the piezoelectric coefficient modulation has been achieved and the acoustic resonances up to 9.8 GHz were demonstrated. The impact of the low electrical field on the orientation of the ferroelectric films prepared by pulsed laser deposition has been analysed based on the theory of heterogeneous nucleation of ferroelectrics under the influence of the applied electric field.

(PT) in ambients of oxygen, nitrogen, and argon was studied by using a CCD camera. Two optical filters with different transmittance bands were used to identify the excitation, dissociation, ionization, and, especially, the chemical reactions in the plume. The results show that the atomic processes and chemical reaction mechanisms in the plume formed in active oxygen are very different from those formed in inert argon and nitrogen. It is proposed that the chemical reactions between ablated metal species and ambient oxygen are initiated by the strong shock wave formed during the propagation of the PT plume.

Oriented LiNbO3 thin films have been prepared by pulsed laser deposition on fused silica substrates under a proper low electric field. The as-grown films were characterized by means of X-ray diffraction θ–2θ scans, X-ray photo-electron spectrometry and atomic force microscopy. Significant effects of the substrate temperature and magnitude of the applied electric field on the orientation of the films are revealed, demonstrating the preferred electric field of ∼7 V/cm and substrate temperature of 600°C. Drastic influence of the substrate temperature on the stoichiometry of the thin films is also shown. The as-prepared thin films show quite good surface quality.

With the advantages of in situ analysis and high surface sensitivity, surface-enhanced infrared absorption spectroscopy in attenuated total reflection mode (ATR-SEIRAS) combined with electrochemical methods has been employed to examine the interfacial direct electron transfer activity and adsorption kinetics of cytochrome c (cyt c). This work presents data on cyt c adsorption onto negatively charged mercaptohexanoic acid (MHA) and positively charged 6-amino-1-hexanethiol (MHN) self-assembled monolayers (SAMs) on gold nanofilm surfaces. The adsorbed cyt c displays a higher apparent electron transfer rate constant (33.5 ± 2.4 s(-1)) and apparent binding rate constant (73.1 ± 5.2 M(-1) s(-1)) at the MHA SAMs surface than those on the MHN SAMs surface. The results demonstrate that the surface charge density determines the protein adsorption kinetics, while the surface charge character determines the conformation and orientation of proteins assembled which in turn affects the direct electron transfer activity.