Transport, location, and quantal release monitoring of single cells on a microfluidic device

A novel microfluidic device has been developed for on-chip transport, location, and quantal release monitoring of single cells. The microfluidic device consists of a plate of PDMS containing channels for introducing cells and stimulants and a glass substrate into which a cell micro-chamber was etched. The two tightly reversibly sealed plates can be separated for respective cleaning, which significantly extends the lifetime of the microchip that is frequently clogged in cell analysis experiments. Using hydraulic pressure, single cells were transported and located on the microfluidic chip. After location of a single PC12 cell on the microfluidic chip, the cell was stimulated by nicotine that was also introduced through the micro-channels, and the quantum release of dopamine from the cell was amperometricly detected with our designed carbon fiber microelectrode. The results have demonstrated the convenience and efficiency of using the microfluidic chip for monitoring of quantal release from single cells and have offered a facile method for the analysis of single cells on microfluidic devices.     

Dynamic cell fractionation and transportation using moving dielectrophoresis

This study presents a new cell manipulation method using a moving dielectrophoretic force to transport or fractionate cells along a microfluidic channel. The proposed moving dielectrophoresis (mDEP) is generated by sequentially energizing a single electrode or an array of electrodes to form an electric field that moves cells continuously along the microchannel. Cell fractionation is controlled by the applied electrical frequency, and cell transportation is controlled by the interelectrode activation time. The applicability of this method was demonstrated to simultaneously fractionate and transport Saccharomyces cerevisiae yeast cells, both viable and nonviable, by operating at conditions under which the cells were subjected to positive and negative dielectrophoresis, respectively. Compared to the conventional dielectrophoresis (cDEP and traveling wave dielectrophoresis (twDEP), moving dielectrophoresis allows cells to be separated on the basis of the real part of the Clausius-Mossotti factor, as in cDEP, but yet allows the direct transportation of separated cells without using fluid flow, as in twDEP. This dielectrophoresis technique provides a new way to manipulate cells and can be readily implemented on programmable multielectrode devices.     

Simultaneous on-chip DC dielectrophoretic cell separation and quantitative separation performance characterization

Through integration of a MOSFET-based microfluidic Coulter counter with a dc-dielectrophoretic cell sorter, we demonstrate simultaneous on-chip cell separation and sizing with three different samples including 1) binary mixtures of polystyrene beads, 2) yeast cells of continuous size distribution, and 3) mixtures of 4T1 tumor cells and murine bone marrow cells. For cells with continuous size distribution, it is found that the receiver operator characteristic analysis is an ideal method to characterize the separation performance. The characterization results indicate that dc-DEP separation performance degrades as the sorting throughput (cell sorting rate) increases, which provides insights into the design and operation of size-based microfluidic cell separation.     

Ultrahigh‐Areal‐Capacitance Flexible Supercapacitor Electrodes Enabled by Conformal P3MT on Horizontally Aligned Carbon‐Nanotube Arrays

Nanocarbon electronic conductors combined with pseudocapacitive materials, such as conducting polymers, display outstanding electrochemical properties and mechanical flexibility. These characteristics enable the fabrication of flexible electrodes for energy‐storage devices; that is, supercapacitors that are wearable or can be formed into shapes that are easily integrated into vehicle parts. To date, most nanocarbon materials such as nanofibers are randomly dispersed as a network in a flexible matrix. This morphology inhibits ion transport, particularly under the high current density necessary for devices requiring high power density. Novel flexible densified horizontally aligned carbon nanotube arrays (HACNTs) with controlled nanomorphology for improved ion transport are introduced and combined with conformally coated poly(3‐methylthiophene) (P3MT) conducting polymer to impart pseudocapacitance. The resulting P3MT/HACNT nanocomposite electrodes exhibit high areal capacitance of 3.1 F cm^?2 at 5 mA cm^?2, with areal capacitance remaining at 1.8 F cm^?2 even at a current density of 200 mA cm^?2. The asymmetric supercapacitor cell also delivers more than 1–2 orders of magnitude improvement in both areal energy and power density over state‐of‐the‐art cells. Furthermore, little change in cell performance is observed under high strain, demonstrating the mechanical and electrochemical stability of the electrodes.     

燃料电池电极板材料工艺发展趋势

电极板是燃料电池的关键核心部件,起到分隔气体、提供反应界面、传导电流的作用。根据燃料电池应用工况的不同,电极板的材料选择与制造工艺路线也有所不同。材料工艺是决定燃料电池设计、质量、成本的核心要素。着重论述了金属、石墨、树脂作为电极材料的工艺路线。针对金属电极板材料,论述了车载、航空航天2种工况下不锈钢、钛材的成形设计准则、工艺路线、产品性能,并分析比较了不同成形方法中设备、模具工装和工艺路线的适用性。针对石墨电极材料,对比了硬石墨一次模压成形和柔性板石墨模压成形2种工艺,并根据各自的基材状态选择了合适的工艺路线,同时根据工艺路线的特点分析了产品的优缺点。在复合材料中主要选择了金属、石墨、树脂3种材料,根据制备原理,复合材料双极板有结构复合电极、材料复合电极和工艺复合电极3个研究方向。在结构复合电极方面,主要论述了石墨与金属复合的设计思路和结构特点;在材料复合电极方面,主要论述了热固性树脂和热塑性树脂与石墨复合的工艺路线和产品特点;在工艺复合电极方面,主要论述了微型燃料电池极板的制造理念和方法,并借鉴了微机械加工工艺路线,设计制造了复合工艺极板。最后展望了燃料电池电极板的箔材研发方向、级...     

Skin‐Like Stretchable Fuel Cell Based on Gold‐Nanowire‐Impregnated Porous Polymer Scaffolds

Skin‐like energy devices can be conformally attached to the human body, which are highly desirable to power soft wearable electronics in the future. Here, a skin‐like stretchable fuel cell based on ultrathin gold nanowires (AuNWs) and polymerized high internal phase emulsions (polyHIPEs) scaffolds is demonstrated. The polyHIPEs can offer a high porosity of 80% yet with an overall thickness comparable to human skin. Upon impregnation with electronic inks containing ultrathin (2 nm in diameter) and ultrahigh aspect‐ratio (>10 000) gold nanowires, skin‐like strain‐insensitive stretchable electrodes are successfully fabricated. With such designed strain‐insensitive electrodes, a stretchable fuel cell is fabricated by using AuNWs@polyHIPEs, platinum (Pt)‐modified AuNWs@polyHIPEs, and ethanol as the anode, cathode, and fuel, respectively. The resulting epidermal fuel cell can be patterned and transferred onto skin as “tattoos” yet can offer a high power density of 280 µW cm^?2 and a high durability (>90% performance retention under stretching, compression, and twisting). The results presented here demonstrate that this skin‐thin, porous, yet stretchable electrode is essentially multifunctional, simultaneously serving as a current collector, an electrocatalyst, and a fuel host, indicating potential applications to power future soft wearable 2.0 electronics for remote healthcare and soft robotics.     

Bio‐microfluidics: Biomaterials and Biomimetic Designs

Bio‐microfluidics applies biomaterials and biologically inspired structural designs (biomimetics) to microfluidic devices. Microfluidics, the techniques for constraining fluids on the micrometer and sub‐micrometer scale, offer applications ranging from lab‐on‐a‐chip to optofluidics. Despite this wealth of applications, the design of typical microfluidic devices imparts relatively simple, laminar behavior on fluids and is realized using materials and techniques from silicon planar fabrication. On the other hand, highly complex microfluidic behavior is commonplace in nature, where fluids with nonlinear rheology flow through chaotic vasculature composed from a range of biopolymers. In this Review, the current state of bio‐microfluidic materials, designs and applications are examined. Biopolymers enable bio‐microfluidic devices with versatile functionalization chemistries, flexibility in fabrication, and biocompatibility in vitro and in vivo. Polymeric materials such as alginate, collagen, chitosan, and silk are being explored as bulk and film materials for bio‐microfluidics. Hydrogels offer options for mechanically functional devices for microfluidic systems such as self‐regulating valves, microlens arrays and drug release systems, vital for integrated bio‐microfluidic devices. These devices including growth factor gradients to study cell responses, blood analysis, biomimetic capillary designs, and blood vessel tissue culture systems, as some recent examples of inroads in the field that should lead the way in a new generation of microfluidic devices for bio‐related needs and applications. Perhaps one of the most intriguing directions for the future will be fully implantable microfluidic devices that will also integrate with existing vasculature and slowly degrade to fully recapitulate native tissue structure and function, yet serve critical interim functions, such as tissue maintenance, drug release, mechanical support, and cell delivery.     

Microfluidic cell electroporation using a mechanical valve

A microfluidic electroporation technique is demonstrated based on the operation of an elastomeric valve in a poly(dimethylsiloxane) (PDMS) fabricated microchip and a common dc power supply. The pulse needed for permeabilization of the cell membrane is generated by temporarily interrupting the circuit using the valve. The electropermeabilization of suspended and adherent Chinese hamster ovary cells with green DNA dye SYTOX is demonstrated. The technique eliminates the cost and complexity associated with a pulse generator and microfabricated electrodes that are often involved in microscale electroporation devices. It also offers the potential of integrating electroporation as a unit operation in large-scale microfluidic systems with the increasing application of elastomeric valves in these systems.     

Discontinuous Nanoporous Membranes Reduce Non‐Specific Fouling for Immunoaffinity Cell Capture

The microfluidic isolation of target cells using adhesion‐based surface capture has been widely explored for biology and medicine. However, high‐throughput processing can be challenging due to interfacial limitations such as transport, reaction, and non‐specific fouling. Here, it is shown that antibody‐functionalized capture surfaces with discontinuous permeability enable efficient target cell capture at high flow rates by decreasing fouling. Experimental characterization and theoretical modeling reveal that “wall effects” affect cell–surface interactions and promote excess surface accumulation. These issues are partially circumvented by reducing the transport and deposition of cells near the channel walls. Optimized microfluidic devices can be operated at higher cell concentrations with significant improvements in throughput.     

Microfluidic system for planar patch clamp electrode arrays

We present a microfluidic system integrated with disposable cell interface partitions for simultaneous patch clamp recordings. Glass-supported poly(dimethylsiloxane) (PDMS) partitions, having a 2 microm air-blown aperture, were reversibly sealed to a microfluidic system including PDMS channels with isolation valves and microfabricated Ag/AgCl electrodes. Gigaseal recordings from RBL-1 cells were obtained with a 24% success rate. Simultaneous whole cell recordings from valve-isolated electrodes were obtained.     

On-chip amperometric measurement of quantal catecholamine release using transparent indium tin oxide electrodes

Carbon-fiber amperometry has been extensively used to monitor the time course of catecholamine release from cells as individual secretory granules discharge their contents during the process of quantal exocytosis, but microfabricated devices offer the promise of higher throughput. Here we report development of a microchip device that uses transparent indium tin oxide (ITO) electrodes to measure quantal exocytosis from cells in microfluidic channels. ITO films on a glass substrate were patterned as 20-mum-wide stripes using photolithography and wet etching and then coated with polylysine to facilitate cell adherence. Microfluidic channels (100 mum wide by 100 mum deep) were formed by molding poly(dimethylsiloxane) (PDMS) on photoresist and then reversibly sealing the PDMS slab to the ITO-glass substrate. Bovine adrenal chromaffin cells were loaded into the microfluidic channel and adhered to the ITO electrodes. Cells were stimulated to secrete by perfusing a depolarizing "high-K" solution while monitoring oxidation of catecholamines on the ITO electrode beneath the cell using amperometry. Amperometric spikes with charges ranging from 0.1 to 1.5 pC were recorded with a signal-to-noise ratio comparable to that of carbon-fiber electrodes. Further development of this approach will enable high-throughput measurement of quantal catecholamine release simultaneously with optical cell measurements such as fluorescence.     

Fabrication–microstructure–performance relationships of reversible solid oxide fuel cell electrodes–review

Abstract

A reversible solid oxide fuel cell system can act as an energy storage device by storing energy in the form of hydrogen and heat, buffering intermittent supplies of renewable electricity such as tidal and wave generation. The most widely used electrodes for the cell are lanthanum strontium manganate–yttria stabilised zirconia and Ni–yttria stabilised zirconia. Their microstructure depends on the fabrication techniques, and determines their performance. The concept and efficiency of reversible solid oxide fuel cells are explained, along with cell geometry and microstructure. Electrode fabrication techniques such as screen printing, dip coating and extrusion are compared according to their advantages and disadvantages, and fuel cell system commercialisation is discussed. Modern techniques used to evaluate microstructure such as three-dimensional computer reconstruction from dual beam focused ion beam–scanning electron microscopy or X-ray computed tomography, and computer modelling are compared. Reversible cell electrode performance is measured using alternating current impedance on symmetrical and three electrode cells, and current/voltage curves on whole cells. Fuel cells and electrolysis cells have been studied extensively, but more work needs to be done to achieve a high performance, durable reversible cell and commercialise a system.     

Fuel cells ∼ a survey Part: 1

This paper is presented in three parts; in Part I, the nature, history and types of fuel cell are outlined, and their advantages and applications noted. Fuels and oxidants are surveyed and types of electrolyte are described. Part II defines the main parameters on which the successful operation of a fuel cell depend and reviews aspects of design which have been used in attempts to improve these parameters. In Part III the concept of non-porous gas-permeable oxygen electrodes for fuel cells is developed; some experimental results are reported using such electrodes fabricated from electrically conductive silicone rubber and potentially useful areas are indicated for future investigation.     

Experimental Investigation of Performance of a Miniature Direct Methanol Fuel Cell in Short-Term Microgravity

Experimental study of a liquid fed direct methanol fuel cell has been conducted in different gravity environments. A small single cell with 5 cm × 5 cm active area has single serpentine channel on the graphite cathode polar plate and 11 parallel straight channels on the graphite anode flow bed. Cell voltage and current have been measured and two-phase flow in anode channels has been in situ visually observed. The experimental results indicate that the effect of gravity on power performance of the direct methanol fuel cell is large when the concentration polarization governs fuel cells operation. Gravitational effect becomes larger at higher current density. Increasing methanol feeding molarity is conducive to weaken the influence of gravity on performance of liquid fed direct methanol fuel cells. Increasing feeding flow rate of methanol solution from 6 to 15 ml/min could reduce the size of carbon dioxide bubbles, while the influence of gravity still exist. Transport phenomena inside direct methanol fuel cells in microgravity is also analyzed and discussed.     

TiO2 thin film encapsulated ZnO nanorod and nanoflower dye sensitized solar cells

The performance of dye-sensitized solar cells based on ZnO nanorods and nanoflowers coated with thin shells of TiO₂ thin film prepared by sol–gel deposition are described. It is found that shells act as insulating barriers that improve cell open-circuit voltage and short-circuit current density. The superior performance of the ZnO–TiO₂ core–shell cells is a result of a radial electron transport within each ZnO nanorods and nanoflowers that decreases the rate of recombination and percolation of the electron in these devices.     

Electrochemical assessment of the interaction of microbial living cells and carbon nanomaterials

This work considers the effects of various carbon nanomaterials and fibres on bioelectrocatalytic and respiratory activity of bacterial cells during the oxidation of ethanol in the presence of an electron transport mediator. Gluconobacter oxydans sbsp. industrius VKM B‐1280 cells were immobilised on the surfaces of graphite electrodes and had an adsorption contact with a nanomaterial (multi‐walled carbon nanotubes, thermally expanded graphite, highly oriented pyrolytic graphite, graphene oxide, reduced graphene oxide). The electrochemical parameters of the electrodes (the polarisation curves, the value of generated current at the introduction of substrate, the impedance characteristics) were measured in two‐electrode configuration. Modification by multi‐walled carbon nanotubes led to the increase of microbial fuel cell (MFC) electric power by 26%. The charge transfer resistance of modified electrodes was 47% lower than unmodified ones. Thermally expanded and pyrolytic graphites had a slight negative effect on the electrochemical properties of modified electrodes. The respiratory activity of bacterial cells did not change in the presence of nanomaterials. The data can be used in the development of microbial biosensors and MFC electrodes based on Gluconobacter cells.Inspec keywords: nanofabrication, catalysis, microorganisms, adsorption, charge exchange, microbial fuel cells, electrochemical electrodes, graphite, graphene, oxidation, multi‐wall carbon nanotubes, cellular biophysicsOther keywords: reduced graphene oxide, electrochemical parameters, two‐electrode configuration, multiwalled carbon nanotubes, microbial fuel cell, respiratory activity, bacterial cells, microbial biosensors, MFC electrodes, microbial living cells, electron transport mediator, graphite electrodes, adsorption contact, highly oriented pyrolytic graphite, Gluconobacter oxydans sbsp. industrius VKM B‐1280 cells, polarisation curves, bioelectrocatalytic activity, ethanol, thermally expanded graphite, charge transfer resistance, C     

Materials development for intermediate-temperature solid oxide electrochemical devices

One of the major challenges in developing electrochemical devices for energy generation has been the identification and development of materials with outstanding performance at reduced (intermediate) temperatures (500–700 °C), increasing the durability and lowering the cost of the device. A solid-state electrochemical cell is in outline a simple device consisting of three components: anode, electrolyte and cathode. The function of each component is critical to cell performance, and as interest in fuel cells and electrolysers has gathered pace, many materials have been evaluated as functional components of these cells. Typically, the requirement for new materials development has been the drive to lower operation temperature, overcoming sluggish reaction kinetics in existing materials. Novel materials for the functional components of both electrolysers and fuel cells are introduced, with emphasis placed on the air electrode and electrolyte, with the potential of new classes of materials discussed, including layered materials, defect fluorites and tetrahedrally coordinated phases. Furthermore, the opportunity presented by thin film deposition to characterize anisotropic transport in materials and develop devices based on thin films is discussed.     

Discovering Reactant Supply Pathways at Electrode/PEM Reaction Interfaces Via a Tailored Interface-Visible Characterization Cell

In situ and micro-scale visualization of electrochemical reactions and multiphase transports on the interface of porous transport electrode (PTE) materials and solid polymer electrolyte (SPE) has been one of the greatest challenges for electrochemical energy conversion devices, such as proton exchange membrane electrolyzer cells (PEMECs), CO₂ reduction electrolyzers, PEM fuel cells, etc. Here, an interface-visible characterization cell (IV-CC) is developed to in situ visualize micro-scaled and rapid electrochemical reactions and transports in PTE/SPE interfaces. Taking the PEMEC of a green hydrogen generator as a study case, the unanticipated local gas blockage, micro water droplets, and their evolution processes are successfully visualized on PTE/PEM interfaces in a practical PEMEC device, indicating the existence of unconventional reactant supply pathways in PEMs. Further comprehensive results reveal that PEM water supplies to reaction interfaces are significantly impacted with current densities. These results provide critical insights about the reaction interface optimization and mass transport enhancement in various electrochemical energy conversion devices.     

Electrochemical photovoltaic cells for solar energy conversion

Photoelectrochemical cells have attracted much more attention recently due to their feasibility as low-cost solar energy conversion devices and hence a number and variety of papers have appeared. Although some review papers have been published, no comprehensive review of electrochemical photovoltaic cells has been made. The present review is devoted to a survey of most of the dimensions of ECPV cells.Starting with photoelectrochemical processes, relevant theoretical background is presented including redox potentials, interface of the semiconductor-liquid junction and Butler-Volmer relation, etc. Much emphasis is given to the requirements of semiconductor electrodes, electrolytes, counter electrods and various cell configurations in ECPV cells. Results on photocorrosion, stability, etc. of the electrodes and the effect of temperature on the performance of the ECPV cell are discussed. Up-to-date data on various ECPV cells are presented and the current situation is discussed. In the light of this, various new materials are attractive. Finally, results on ECPV storage cells and their potential applications are discussed.     

微型直接甲醇燃料电池阳极流场结构

针对微型直接甲醇燃料电池(DMFC)阳极传质效率低和性能差等问题,对DMFC阳极流场结构进行了研究.利用MEMS技术实现了具有点形、平行和蛇形等阳极流场结构的硅基自呼吸式DMFC,测试对比结果表明单蛇形流场结构性能要优于其他几种流场;另外,对单蛇形流场结构参数进行了优化,结果表明当流道宽度∶脊的宽度∶流道长度为2∶3∶254时,电池性能达到最佳.在此基础上,为了改善反应物到催化层的传质效率和提高性能,提出了一种渐缩式单蛇形流场结构,其电池最大输出功率密度达到15.41 mW/cm2,比传统等宽式单蛇形流场提高了将近35%,为便携式微能源系统的应用开发奠定了基础.