bluuebunny/crossref_metadata_2025 huggingface dataset:
Regular Surface Texture Generated by Special Grinding Process
Authors: Stȩpień Piotr
Published: January 2009

Most of the methods for generating regular surface texture (RST) consist of shaping a set of regular grooves (cavities) arranged in a regular way. This paper presents possibilities for regular surface texture generation by so-called “pattern grinding” with the wheel prepared in a special way. The simple variant of the method involves grinding with the wheel having helical grooves. The grooves shaped on the work material are the result of specific wheel surface reproduction. The ratio between work-material feed and wheel speed is an important factor, determining the layout of the grooves generated on the work-material and the shape of the groove sides. Surface texture consists of two components: deterministic, resulting from the nominal wheel active surface, and random, resulting from the random shape and arrangement of abrasive grains. The limited contribution of the random component of surface texture is discussed based on the ratio between the undeformed chip thickness and the sizes of the grooves. Kinematical analysis of the wheel reproduction process is performed for description of nominal surface texture. Experimental results of flat and cylindrical surfaces, obtained with pattern grinding are also provided. Two critical values of the ratio between work-material feed and wheel speed were derived, and three ranges of this ratio are discussed. The kinematical approach provided relationships between input data of the process (wheel shape and grinding parameters) and nominal groove dimensions and groove layout. The geometrical characteristics of the work-material nominal surface texture are presented for each of the three types of surface texture. It is important to ensure that the work feeds are greater than the lower critical value. For achievable work feeds the shape of the sides of the grooves is cycloid. Experiments revealed the limited contribution of the random component of the surface structure of the work material. Random arrangement of abrasive grains is important only at local (micro-) level and affects the roughness of groove bottoms, while the dimensions and arrangement of the grooves are affected only to a minimal degree.
The Upcoming Generation of Common Rail Injection Systems for Large Bore Engines From L’Orange GmbH
Authors: Jorach Rainer W. , Ressel Horst , Scheibe Wolfgang , Prillwitz Rolf , Bakaj Leo
Published: January 2009

In August 1997 L’Orange GmbH launched the first electronic common rail injection system in the world for application to mtu and DDC series 4000. This had a major impact on the entire Diesel engine industry as it made possible the highest improvements in fuel efficiency, exhaust-emissions and black smoke, power and torque. In the past five years, a complete range of common rail injection systems for Diesel, micro pilot, water and heavy fuel oil injection between 100 and 1050 kW/cyl have been introduced to the market by L’Orange. Design and performance of these injection system types will be reviewed in brief. The evaluation of these systems including comparison of advantages and disadvantages led to the next generation concepts and design. One of the next generation type heavy fuel oil common rail injection systems will be presented in detail.
Simulation and Analysis of Combustion and Heat Transfer in Low Heat Rejection Diesel Engine Using Two Zone Combustion Model and Different Heat Transfer Models
Authors: Tamilporai P. , Chandrasekaran S. , Baluswamy N. , Jancirani J.
Published: January 2009

The quest for increasing the efficiency of an internal combustion engine has been going on ever since the invention of this reliable work equipment. In recent times much attention has been focused on achieving higher thermal efficiency by reducing the heat loss to the surroundings by the application of “low heat rejection” concept using ceramic coating for engine components or ceramic components itself. In this direction, the present analysis focused on the formulation and development of a two zone combustion model for the prediction of combustion, heat release and performance of the conventionally Water cooled and low heat rejection engines. The low heat rejection concept is introduced in this model by developing and formulating a wall heat transfer model to consider the effect of instantaneous inside surface temperature on combustion and heat release of an LHR engine. The gas wall heat transfer by means of convection and radiation is calculated using various gas wall heat transfer models. The predictions by the computer model and experimental findings are demonstrated. The capability of this model and the comparison of the predicted results with experimental findings are highly satisfactory.
Computational Modeling of Natural Gas Injection in a Large Bore Engine
Authors: Kim Gi-Heon , Kirkpatrick Allan , Mitchell Charles
Published: January 2009

The topic of this paper is the computational modeling and experimental visualization of gas injection in a large bore engine. The injection process is accomplished through the use of a mechanically or electrically controlled poppet valve. The objective of the paper is to more fully understand the significance of the poppet valve and the piston top in controlling the mixing of the injected fuel with the air in the cylinder. In this paper, the flow past the poppet valve into the engine cylinder is computed using computational fluid dynamics (CFD) for both a low (4 bar) and a high pressure (34 bar) injection process using unshrouded and shrouded valves. Flow visualization using planar laser induced fluorescence (PLIF) is used to visualize the actual fluid flow. The results indicate that for low pressures the gas flow around the poppet valve collapses downstream of the poppet. At high pressure, the gas flow does not collapse, but flows along the cylinder wall, producing poor mixing in the cylinder. To obtain satisfactory fluid flow at high pressure, the results indicated a shroud should be employed around the poppet valve to direct the gas into the center of the cylinder. Additional computations show that at top dead center, the flammable mixture and fuel mass fraction for the high-pressure injection are significantly greater than for the low-pressure injection.
Numerical Analysis and Experimental Investigation of a Common Rail Type Diesel Injector
Authors: Coppo Marco , Dongiovanni Claudio , Negri Claudio
Published: January 2009

A production common rail type injector has been investigated via numerical simulation and experimentation. The functioning principle of the injector has been carefully analysed so as to obtain a mathematical model of the device. A zero-dimensional approach has been used for modelling the injector, thus considering the variables as function of time only. The analysis of the hydraulic part of the injector resulted in the definition of an equivalent hydraulic scheme, on which basis both the equations of continuity in chambers and flow through nozzles were written. The moving mechanical components of the injector, such as needle, pressure rod and control valve have been modelled using the mass-spring-damper scheme, thus obtaining the equation governing their motion. An electromagnetic model of the control valve solenoid has also been realized, in order to work out the attraction force on the anchor, generated by the electric current when flowing into its coil. The model obtained has been implemented using the Matlab® toolbox Simulink® and solved by means of the NDF (Numerical Differentiation Formulas) implicit scheme of the second order accuracy, suitable for problems with high level of stiffness. The experimental investigation on the common-rail injection system was performed on a test bench at some standard test conditions. Electric current flowing through the injector coil, oil pressure at the injector inlet, injection rate, needle lift and control valve lift were gauged and recorded during several injection phases. The mean reflux-flow rate and the mean quantity of fuel injected per stroke were also measured. Temperature and pressure of the feeding oil, as well as pressure in the rail were continuously controlled during the experimental test. The numerical and experimental results were compared. The model was then used to investigate the effect of control volume feeding and discharge holes and of their inlet fillet, as well as the effect of the control volume capacity, on the injector performance.
Influence of Spray Velocity and Structure on the Air Entrainment in the Primary Breakup Zone of High Pressure Diesel Sprays
Authors: Schugger Christian , Renz Ulrich
Published: January 2009

Nozzle geometry and rail pressure influence the gas-liquid momentum transfer and the turbulent dispersion in the primary breakup zone of high-pressure Diesel sprays, and consequently the combustion processes. To investigate these phenomena, different measuring techniques have been used. The spray structure is visualized using shadowgraphy and scattered light imaging, and the axial velocities in the dense spray region have been measured using a Laser Correlation Velocimeter. Gas velocities are measured using Particle Image Velocimetry. It is found that the dimensionless velocities (related to the frictionless velocity) are independent of the injection pressure and the nozzle geometry. However the momentum transfer between the liquid phase and the surrounding air strongly depends on the spray structure. Here a sharp edged nozzle inlet promotes cavitation and turbulence levels in the nozzle which leads to stronger breakup and significantly enhanced air entrainment.
Experimental Investigation of the Turbulent Flow Field of Vaporizing Diesel-Sprays
Authors: Staudt Michael , Meingast Ulrich , Renz Ulrich
Published: January 2009

In this work investigations of the flow-field inside and around a heated, vaporizing diesel-fuel-jet are presented. The experiments are carried out in a high-pressure-chamber at elevated temperatures using a commercial Bosch-Common-Rail Diesel-injection system. The pressure and temperature inside the chamber are chosen according to the conditions in a real engine cylinder after compression. Droplet diameters and velocities inside the fuel jet are measured by means of Phase-Doppler-Anemometry (PDA). In order to obtain the velocities of the gas phase very close to the free penetrating fuel jet by Laser-Doppler-Anemometry (LDA), the air inside the chamber is seeded with Titan-Dioxide (TiO2)-particles. Turbulence values like RMS and length scales are derived from these measurements. In addition to these spatially limited measurements the global flow-field around the penetrating fuel-jet is observed by two-dimensional measurements with Particle-Image-Velocimetry (PIV). From the nozzle exit up to 2/3 of the whole penetration length an air flow perpendicular to the spray axis can be detected. This air-flow into the spray provides the heat transfer and vaporization of the fuel-droplets. The fuel jet contains a high droplet concentration which leads to high intensities in the resulting PIV-images from which discrete spray contours can be calculated. By means of the gas-flow velocity components at this contour the total mass of the absorbed air is calculated. This mass is compared at three injection pressures: 80, 100 and 135 MPa. Further experiments concentrate on a spray impinging straight onto a flat wall. The wall jet leads to additional contributions of air absorption into regions with high droplet concentrations.
Strategies for Reduced NOx Emissions in Pilot-Ignited Natural Gas Engines
Authors: Krishnan Sundar R. , Srinivasan Kalyan K. , Gong Weidong , Fiveland Scott , Singh Satbir , Bell Stuart R. , Midkiff K. Clark , Willi Martin
Published: January 2009

The performance and emissions of a single-cylinder, natural gas fueled engine using a pilot ignition strategy have been investigated. Small diesel pilots (2–3 percent on an energy basis), when used to ignite homogeneous natural gas-air mixtures, are shown to possess the potential for reduced NOx emissions while maintaining good engine performance. The effect of pilot injection timing, intake charge pressure, and charge temperature on engine performance and emissions with natural gas fueling was studied. With appropriate control of the above variables, engine-out brake specific NOx emissions could be reduced to the range of 0.07–0.10 g/kWh from the baseline diesel (with mechanical fuel injection) value of 10.5 g/kWh. For this NOx reduction, the decrease in fuel conversion efficiency from the baseline diesel value was approximately 1–2 percent. Total unburned hydrocarbon (HC) emissions and carbon monoxide (CO) emissions were higher with natural gas operation. Heat release schedules obtained from measured cylinder pressure data are also presented. The importance of pilot injection timing and inlet conditions on the stability of engine operation and knock are also discussed.
Effects of Turbine Blade Tip Clearance on Turbocharger Performance: An Experimental Investigation
Authors: Keshavarz A. , Chapman K. S. , Shultz J. , Kuiper D. G.
Published: January 2009

Rising fuel costs and increasingly stringent emission standards push engineers to develop more efficient turbo-machinery. Reducing turbocharger turbine tip clearance is one method of improving turbine performance, thereby improving overall engine operation. By using tip seals or abradable seals, reduction of this clearance is possible. Metco 314 NS material was applied to an Elliot-H type turbocharger turbine shroud to reduce the cold clearance from 0.762 mm (0.030 inch) to 0.457mm (0.018 inch). Two separate yet virtually identical performance tests were conducted at speeds of 13,000 rpm, 15,000 rpm, and 17,000 rpm on the turbocharger. The first test established the efficiency condition of the turbocharger with the tip seal installed. The second was to quantify a decrease in efficiency, if present, after the tip seal was removed. Both tests were conducted as identically as possible. The average amount of available energy not utilized with the tip seal removed was 30.26 kW at 13,000 rpm, 51.42 kW at 15,000 rpm and 45.71 kW at 17,000 rpm.
Modeling of NOx Emissions Using a Super-Extended Zel’dovich Mechanism
Authors: Yang Huateng , Krishnan Sundar R. , Srinivasan Kalyan K. , Midkiff K. Clark
Published: January 2009

A kinetic model for NOx production has been developed to predict NOx emissions. The reaction scheme is a modified super-extended Zel’dovich mechanism (SEZM), which includes 43 reactions and 20 species instead of just the three reactions typically used in the extended Zel’dovich mechanism. The NOx emissions predicted by both mechanisms are compared using two separate models. First, a theoretical investigation of the two mechanisms is made for an SI engine using prescribed temperature and pressure histories. Then each of the two mechanisms is combined with a phenomenological combustion model for a single-cylinder Caterpillar 3400 series diesel engine to calculate the NOx emissions. The predictions from both mechanisms are compared with experimental results. It is shown that the SEZM can predict NOx emissions more accurately than the extended Zel’dovich mechanism. Results show that the SEZM increases the predicted NOx by about 25 percent. The difference between the two models is more pronounced for lean combustion, in which NO2 and NH play an important role in the NOx formation. In addition, the effects of several parameters on diesel engine NOx production are investigated. The super-extended Zel’dovich mechanism for NOx formation is expected to be more appropriate for lean combustion, such as in diesel or natural gas engines and other engines that typically operate at lean conditions.
Missing Combustion Diagnosis: Distinguishing Between Misfire and Misfuel
Authors: Corti Enrico
Published: January 2009

On-Board Diagnostics (OBD) regulations impose missing combustions detection within a wide portion of the engine operating range. Missing combustions can be caused either by ignition (misfire) or injection (misfuel) system failures. Missing combustions can damage the catalyst and cause abrupt pollutants increases (especially HC), but misfuels are not as detrimental as misfires, both from the emissions and the after treatment system life point of view. It would be important for the Electronic Control Unit (ECU) to be informed not only about the fault event, but also about its type, for the purpose of setting the right recovery strategy. The aim of this paper is to analyze missing combustion phenomena, in order to find out if a fault recognition strategy able to distinguish between misfire and misfuel can be setup. Different approaches can be found in the literature to diagnose missing combustions: many of them are based on the speed signal analysis, both in time and frequency domains, others use the knock accelerometer signal, or the exhaust manifold pressure information. A Universal Exhaust Gas Oxygen (UEGO) sensor can also be used. Usually diagnosis methodologies consist in observing signals perturbations subsequent to the malfunction event. Observable consequences of missing combustions are, for example, a sudden lack of indicated torque, causing vibrations and speed fluctuations, an increasing in exhaust gases Oxygen content, anomalous exhaust pressure ripples, etc. Many phenomena interact influencing in different ways the engine behavior, during and after the fault event: their effect can depend on the fault cause, thus helping the recognition. The first combustion taking place in the faulty cylinder after a misfire (post-misfiring cycle) usually leads to higher indicated pressure and torque levels if compared to standard values for the same operating conditions, while the same cannot be said for the post-misfueling combustion. On the other side, Air-Fuel Ratio (AFR) assumes different trends during the misfiring and post-misfiring cycles, with respect to misfueling and post-misfueling cycles. A 4 cylinders 1.2 liters spark ignition port injected engine, equipped with a programmable Electronic Control Unit (ECU) has been tested on the test bench, inducing both misfires and misfuels, over a wide engine operating range, while monitoring the engine faulty behavior. Misfire and misfuel-related phenomena have been analyzed showing their “signature” on indicated pressure and torque, engine speed and Air-Fuel Ratio measured signals, in order to define the most reliable recognition strategy.
Two Dimensional Effects in the Lubrication of the Cam-Tappet Contact
Authors: Taraza Dinu , Teodorescu Mircea , Henein Naeim A. , Bryzik Walter
Published: January 2009

The cam-tappet contact experiences very high loads and the lubrication conditions are Elasto-Hydrodynamic (EHD). In EHD lubrication the oil film thickness (OFT) is mainly determined by the entrainment speed of the oil and the oil viscosity. Under the high load present in the cam-tappet contact the OFT reaches very small values in the order of magnitude of a fraction of one micrometer and asperity contacts cannot be avoided. In this situation the friction force has two components, a boundary and a viscous one, and non-Newtonian behavior of the oil prevails. The friction force is determined by the rheological properties of the oil and the geometry of the contact (combined radius of curvature, cam width and combined asperity of the rubbing surfaces). For valve trains with bucket type tappets, the mechanism is design to rotate the tappet during engine operation. In this situation, both the entrainment speed and the radius of curvature are varying along the contact line determining variations in the OFT and, consequently, variations in the contribution of the boundary friction component. Based on a simulation model that considers the tappet spin under the action of the friction force between cam and tappet, and the friction force between tappet and its bore, the entrainment speeds and their directions were calculated along the contact line. It was found that the boundary friction component reaches a maximum value at the inner edge of the cam, at the beginning of the valve-closing event. Because the boundary component of the friction force is mainly responsible for wear, an increased wear of this region should occur. Visual inspection of a used camshaft seems to confirm this finding.
Rotor Dynamic Improvement for a Locomotive Turbocharger
Authors: Rodri´guez He´ctor M. , Furman Anthony H. , Panambur Suresha
Published: January 2009

Turbocharger designs typically incorporate fixed-geometry hydrodynamic bearings. These bearings are known to be prone to exhibit sub-synchronous vibration response. This self-induced sub-synchronous vibration component is due to stiffness cross-coupling in the bearings and is independent of the level of rotor unbalance. This type of vibration has been shown to have the potential to destabilize the rotor-bearing system and inducing rapid growth in the vibration amplitude that could lead to mechanical failure. The present work considers the bearing redesign for a locomotive turbocharger with the objective of eliminating sub-synchronous vibration components by increasing the threshold onset speed with no increase in cost or bearing size. The paper describes the characterization of the original design, the optimization of the new bearing design and the experimental validation. As shown in the results, the optimized bearing configuration eliminated the sub-synchronous vibration component within the turbocharger speed range.
An Experimental Study of Cyclic Variations in a Lean Burn Natural Gas Fuelled Spark Ignition Engine
Authors: Ramesh A. , Tazerout Mohand , Le Corre Olivier
Published: January 2009

This work deals with the nature of cycle by cycle variations in a single cylinder, lean burn, natural gas fuelled spark ignition engine operated at a constant speed of 1500 rev/min under variable equivalence ratio, fixed throttle conditions. Cycle by cycle variations in important parameters like indicated mean effective pressure (IMEP), peak pressure, rate of pressure rise and heat release characteristics were studied. At the lean misfire limit there was a drastic increase in combustion duration. With mixtures leaner than the lean limit, good cycles generally followed poor cycles. However, the vice versa was not true. Cycles that had a high initial heat release rate lead to more complete combustion. A high rate of pressure rise led to a high IMEP. The IMEP of cycles versus their frequency of occurrence was symmetric about the average value when the combustion was good.
S-layer stabilized lipid membranes (Review)
Authors: Schuster Bernhard , Pum Dietmar , Sleytr Uwe B.
Published: January 2009

The present review focuses on a unique bio-molecular construction kit based on surface-layer S-layer proteins as building blocks and patterning elements, but also major classes of biological molecules such as lipids, membrane-active peptides and membrane proteins, and glycans for the design of functional supported lipid membranes. The biomimetic approach copying the supramolecular building principle of most archaeal cell envelopes merely composed of a plasma membrane and a closely associated S-layer lattice has resulted in robust and fluid lipid membranes. Most importantly, S-layer supported lipid membranes spanning an aperture or generated on solid and porous substrates constitute highly interesting model membranes for the reconstitution of responsive transmembrane proteins and membrane-active peptides. This is of particular challenge as one-third of all proteins are membrane proteins such as pore-forming proteins, ion channels, and receptors. S-layer supported lipid membranes are seen as one of the most innovative strategies in membrane protein-based nanobiotechnology with potential applications that range from pharmaceutical high-throughput drug screening over lipid chips to the detection of biological warfare agents.
Formation of supported bacterial lipid membrane mimics
Authors: Merz Christoph , Knoll Wolfgang , Textor Marcus , Reimhult Erik
Published: January 2009

In recent years, a large effort has been spent on advancing the understanding of how surface-supported membranes are formed through vesicle fusion. The aim is to find simple model systems for investigating biophysical and biochemical interactions between constituents of cell membranes and, for example, drugs and toxins altering membrane function. Designing and controlling the self-assembly of model membranes onto sensor substrates thus constitutes an important field of research, enabling applications in, e.g., drug screening, dynamic biointerfaces, artificial noses, and research on membrane-active antibiotics. The authors have developed and investigated the formation of strongly negatively charged supported lipid membranes which systematically mimic bacterial membrane composition on three important biosensor materials: SiO2, TiO2, and indium tin oxide. By tuning the electrostatic interaction through balancing the lipid vesicle charge with the ionic strength of Ca2+ as a fusion promoter, the authors have optimized the self-assembly and obtained new insights into the details of lipid vesicle-surface interaction. The results will be useful for future development and application of specialized lipid membrane surface coatings prepared from complex lipid compositions. The adsorption processes were characterized by a quartz crystal microbalance with dissipation monitoring, optical waveguide lightmode spectroscopy, and fluorescence recovery after photobleaching, which allowed the determination of formation also of nonplanar supported lipid membranes.
Melting and interdigitation of microstructured solid supported membranes quantified by imaging ellipsometry
Authors: Gedig Maja , Faiß Simon , Janshoff Andreas
Published: January 2009

The phase transition of individually addressable microstructured lipid bilayers was investigated by means of noncontact imaging ellipsometry. Two-dimensional membrane compartments were created on silicon substrates by micromolding in capillaries and the phase transition of supported dimyristoylphosphadiylcholine DMPC and dipentadecoylphosphatidylcholine DiC15PC membranes was determined measuring area expansion and thickness of the bilayer as a function of temperature, ethanol concentration, and cholesterol content. Apart from measuring the thermotropic behavior of DMPC on glass slides and silicon wafers, the authors were able to visualize the reversible induction of an interdigitated phase by partitioning of ethanol into the microstructured lipid bilayers. Interdigitation induced by addition of ethanol was measured as a function of cholesterol content and shifts of the main phase transition temperature TM of microstructured DiC15PC were quantified as a function of ethanol concentration. They observed that cholesterol abolishes interdigitation at higher concentrations and found a biphasic behavior of TM as a function of ethanol concentration in good accordance to what is known from vesicles in solution.
Surface supported bilayer platform for studies of lateral association of proteins in membranes (Mini Review)
Authors: Merzlyakov Mikhail , Li Edwin , Hristova Kalina
Published: January 2009

Here, the authors review how surface supported bilayers can be engineered and how Förster resonance energy transfer (FRET) can be used to quantify interactions between transmembrane peptides in these bilayers. The requirements for the surface supported platform are (1) lateral mobility of the peptides, (2) transmembrane orientation of the peptides, and (3) capabilities for FRET measurements. To satisfy these requirements, a new assembly method, termed “directed assembly” was developed. This assembly method could have broad utility in basic studies of proteins in membranes and in biotechnological applications.
Solid supported lipid membranes: New concepts for the biomimetic functionalization of solid surfaces
Authors: Knoll W. , Naumann R. , Friedrich M. , Robertson J. W. F. , Lösche M. , Heinrich F. , McGillivray D. J. , Schuster B. , Gufler P. C. , Pum D. , Sleytr U. B.
Published: January 2009

Surface-layer (S-layer( supported lipid membranes on solid substrates are interfacial architectures mimicking the supramolecular principle of cell envelopes which have been optimized for billions of years of evolution in most extreme habitats. The authors implement this biological construction principle in a variety of layered supramolecular architectures consisting of a stabilizing protein monolayer and a functional phospholipid bilayer for the design and development of new types of solid-supported biomimetic membranes with a considerably extended stability and lifetime — compared to existing platforms — as required for novel types of bioanalytical sensors. First, Langmuir monolayers of lipids at the water/air interface are used as test beds for the characterization of different types of molecules which all interact with the lipid layers in various ways and, hence, are relevant for the control of the structure, stability, and function of supported membranes. As an example, the interaction of S-layer proteins from the bulk phase with a monolayer of a phospholipid synthetically conjugated with a secondary cell wall polymer (SCWP) was studied as a function of the packing density of the lipids in the monolayer. Furthermore, SCWPs were used as a new molecular construction element. The exploitation of a specific lectin-type bond between the N-terminal part of selected S-layer proteins and a variety of glycans allowed for the buildup of supramolecular assemblies and thus functional membranes with a further increased stability. Next, S-layer proteins were self-assembled and characterized by the surface-sensitive techniques, surface plasmon resonance spectroscopy and quartz crystal microbalance with dissipation monitoring. The substrates were either planar gold or silicon dioxide sensor surfaces. The assembly of S-layer proteins from solution to solid substrates could nicely be followed in-situ and in real time. As a next step toward S-layer supported bilayer membranes, the authors characterized various architectures based on lipid molecules that were modified by a flexible spacer separating the amphiphiles from the anchor group that allows for a covalent coupling of the lipid to a solid support, e.g., using thiols for Au substrates. Impedance spectroscopy confirmed the excellent charge barrier properties of these constructs with a high electrical resistance. Structural details of various types of these tethered bimolecular lipid membranes were studied by using neutron reflectometry. Finally, first attempts are reported to develop a code based on a SPICE network analysis program which is suitable for the quantitative analysis of the transient and steady-state currents passing through these membranes upon the application of a potential gradient.
Biosensors based on release of compounds upon disruption of lipid bilayers supported on porous microspheres
Authors: Piyasena Menake E. , Zeineldin Reema , Fenton Kyle , Buranda Tione , Lopez Gabriel P.
Published: January 2009

The authors describe a biosensing concept based on the release of compounds, which are encapsulated within lipid-coated porous silica microspheres, by detergents and toxins that disrupt supported lipid bilayers SLBs on the microspheres. Suspension and microfluidic based methods have been developed to monitor the release of the encapsulated compounds in response to membrane disruption. The authors established that the SLBs on porous microspheres can endure experimental conditions necessary for their incorporation into packed microchannels while maintaining the bilayer integrity and functionality. Model compounds including a nonionic detergent Triton X-100, a membrane active protein (α-hemolysin, and a membrane lytic antimicrobial peptide melittin were successfully utilized to interact with different formulations of SLBs on porous silica microspheres. The results demonstrate the stability of the SLBs on the microspheres for several weeks, and the feasibility of using this system to detect the release of fluorescent dyes as well as other molecular reporters. The latter were detected by their involvement in subsequent biospecific interactions that were detected by fluorescence. This study exemplifies proof of concept for developing new chemical and biochemical sensors and drug delivery systems based on the disruption of lipid membranes coating porous silica microspheres that encapsulate dyes or bioactive compounds.
Micropatterned model biological membranes composed of polymerized and fluid lipid bilayers
Authors: Morigaki Kenichi
Published: January 2009

Micropatterned phospholipid bilayers on solid substrates offer an attractive platform for various applications, such as high-throughput drug screening. The authors have developed a photopolymerization-based methodology for generating micropatterned bilayers composed of polymerized and fluid lipid bilayers. Lithographic photopolymerization of a diacetylene-containing phospholipid (DiynePC) allowed facile fabrication of compartmentalized arrays of fluid lipid membranes. Herein, the authors report on the present state of research and discuss on the prospective application of the model membranes.
Protein tethered lipid bilayer: An alternative mimic of the biological membrane (Mini Review)
Authors: Naumann Renate L. C. , Knoll Wolfgang
Published: January 2009

An overview is given about results obtained so far with an alternative concept of solid-supported tethered lipid bilayers for the functional incorporation of membrane proteins. The incorporated protein itself acts as the tethering molecule resulting in a versatile system where the protein determines the characteristics of submembraneous space. This architecture is achieved through a metal chelating surface, onto which histidine-tagged (his-tagged) membrane proteins are able to bind in a reversible manner. The tethered bilayer membrane is generated by substitution of protein bund detergent molecules with lipids using in situ dialysis or adsorption. Histidine-tagged ctochrome c oxidase is used as a model protein in this study. However, the system should be applicable to all recombinant membrane proteins bearing a terminal his tag. The system is particularly designed, among other surface-analytical techniques, for a combined application of electrochemical and vibrational spectroscopy measurements.
Supported lipid bilayers, tethered lipid vesicles, and vesicle fusion investigated using gravimetric, plasmonic, and microscopy techniques
Authors: Höök Fredrik , Stengel Gudrun , Dahlin Andreas B. , Gunnarsson Anders , Jonsson Magnus P. , Jönsson Peter , Reimhult Erik , Simonsson Lisa , Svedhem Sofia
Published: January 2009

This article summarizes our most recent contributions to the rapidly growing field of supported lipid assemblies with emphasis on current studies addressing both fundamental and applied aspects of supported lipid bilayer (SLB) and tethered lipid vesicles (TLVs) to be utilized in sensing applications. The new insights obtained from combining the quartz crystal microbalance with dissipation monitoring technique with surface plasmon resonance are described, and we also present recent studies in which nanoplasmonic sensing has been used in studies of SLBs and TLVs. To gain full control over the spatial arrangement of TLVs in both two and three dimensions, we have developed a method for site-selective and sequence-specific sorting of DNA-tagged vesicles to surfaces modified with complementary DNA. The combination of this method with nanoplasmonic sensing formats is covered as well as the possibility of using DNA-modified vesicles for the detection of unlabeled DNA targets on the single-molecule level. Finally, a new method for membrane fusion induced by hybridization of vesicle-anchored DNA is demonstrated, including new results on content mixing obtained with vesicle populations encapsulating short, complementary DNA strands.
Surface plasmon optical study of the interfacial phase transition of elastinlike polypeptide grafted on gold
Authors: Xu Fei , Joon Huang Min , Trabbic-Carlson Kimberly , Chilkoti Ashutosh , Knoll Wolfgang
Published: January 2009

The conformational changes in elastinlike polypeptides (ELPs) grafted to a solid/solution interface via different architectures were studied using surface plasmon resonance spectroscopy and surface plasmon field-enhanced fluorescence spectroscopy (SPFS). SPFS provides a simple and convenient optical method to study the influence of the grafting method and the graft density on the conformational changes in ELPs at the solid-solution interface as a function of environmental variables. A typical response of the ELP, consistent with its stimuli responsiveness, was a gradual collapse upon increasing the ionic strength; this effect was inversely correlated with the surface graft density of the ELP.
Structure and properties of soft organic-aqueous interfaces
Authors: Grunze Michael , Pertsin Alexander
Published: January 2009

The interfaces formed by water and aqueous solutions with organic soft matter play an important part in nature and technological applications. Good examples are provided by water in contact with surfactants, self-assembled monolayers, polymers, biomembranes, and other biological matter. A characteristic feature of most soft organic-aqueous interfaces is a deep interpenetration of the aqueous and organic phases, resulting in a wide interfacial region that can formally be regarded as an interphase. The anisotropy, inhomogeneity, thermal disorder, and large extension of the interfacial region in width make the structure and properties of such interfaces difficult to study with the available experimental techniques. The situation is particularly complicated in sandwich-like systems, where water or an aqueous solution is nanoconfined between organic phases. This occurs, for instance, when two biomembranes come close together, so that their interfacial regions interact and intersect.
Simulations of water at the interface with hydrophilic self-assembled monolayers (Review)
Authors: Stevens Mark J. , Grest Gary S.
Published: January 2009

Simulations of water at hydrophilic self-assembled monolayer (SAM) surfaces are especially relevant for biological interfaces. Well-defined, atomically smooth surfaces that can be continuously varied are possible with SAMs. These characteristics enable more accurate measurements than many other surfaces with the added advantage of tailoring the surface to treat specific chemical groups. A fundamental question is how solid surfaces affect the structure and dynamics of water. Measurements of the structure and dynamics of water at solid surfaces have improved significantly, but there remain differences among the experiments. In this article, the authors review simulations of water at the interface with hydrophilic SAMs. These simulations find that while the interfacial water molecules are slower than the bulk water molecules, the interfacial dynamics remains that of a liquid. A major biological application of SAMs is for making coatings resistant to protein adsorption. SAMs terminated with ethylene glycol monomers have proven to be excellent at resisting protein adsorption. Understanding the mechanisms behind this resistance remains an unresolved issue. Recent simulations suggest a new perspective of the role of interfacial water and the inseparable interplay between the SAM and the water.
Protein biochips patterned by microcontact printing or by adsorption-soft lithography in two modes
Authors: Wigenius Jens A. , Fransson Sophia , von Post Fredrik , Inganäs Olle
Published: January 2009

Patterning of proteins is critical to protein biochips. Printing of layers of proteins is well established, as is adsorption of proteins to surfaces properly modified with surface chemical functionalities. The authors show that simple methods based on soft lithography stamps can be used to prepare functional antibody chips through both these routes. Both methods incorporate transfer of the stamp material poly(dimethylsiloxane) (PDMS) to the biochip, whether intended or not intended. The results indicate that microcontact printing of proteins always includes PDMS transfer, thereby creating a possibility of unspecific adsorption to a hydrophobic domain.
Optical sensors based on spectroscopy of localized surface plasmons on metallic nanoparticles: Sensitivity considerations
Authors: Kvasnička P. , Homola J.
Published: January 2009

Surface plasmon resonance (SPR) sensors use two types of surface plasmons: (i) propagating along a metal-dielectric interface and (ii) localized on metallic nano-objects. This article presents theoretical analysis of sensitivity of SPR sensors based on spectroscopy of localized surface plasmons on metallic nanoparticles. Analytical formulas inter-relating bulk and surface refractive index sensitivity with main design parameters are derived using the electrostatic approximation. The effect of particle diameter is accounted for by means of Mie theory. Figures of merit for SPR sensors using localized and propagating surface plasmons are calculated and compared. Although sensors based on spectroscopy of localized surface plasmons on gold spherical particles show promise for detection of processes occurring in the close proximity of the particle surface, their performance is still inferior to that of SPR sensors based on spectroscopy of propagating surface plasmons.
Nanoparticle diffraction gratings for DNA detection on photopatterned glass substrates
Authors: Sendroiu Iuliana E. , Corn Robert M.
Published: January 2009

An ex situ nanoparticle DNA detection assay utilizing DNA-modified nanoparticles attached to DNA monolayer gratings on glass substrates is developed. The assay utilizes the simultaneous hybridization of a single stranded DNA (ssDNA) target molecule to both an amine-modified DNA oligonucleotide attached to an amine-reactive glass surface and a thiol-modified DNA oligonucleotide attached to a 13 nm gold nanoparticle. Surface plasmon resonance imaging measurements are used to characterize the two sequential hybridization adsorption processes employed in the assay, and fluorescence microscopy is used to characterize the formation of DNA monolayer gratings via the photopatterning of the amine-reactive glass slides. First order diffraction measurements utilizing incoherent collimated white light source and a 10 nm bandpass filter centered at 600 nm provided quantitative measurements of target ssDNA down to a concentration of 10 pM. Fourth order diffraction measurements employing a HeNe laser and avalanche photodiode were used to detect target ssDNA adsorption from 10 μl of a solution with a concentration as low as 10 fM, corresponding to 60000 target DNA molecules. This simple yet sensitive grating-based nanoparticle DNA detection assay should be directly applicable for genetic screening, mRNA expression assays, and microRNA profiling.
Water at polar and nonpolar solid walls (Review)
Authors: Sedlmeier Felix , Janecek Jiri , Sendner Christian , Bocquet Lyderic , Netz Roland R. , Horinek Dominik
Published: January 2009

Recent progress in simulating the properties of interfacial water at hard hydrophobic and hydrophilic surfaces is reviewed and compared to results for the air/water interface. The authors discuss static properties such as the equilibrium contact angle, the depletion layer thickness, and the orientation of interfacial water molecules. Relations between these properties, e.g., the relation between the contact angle and the thickness of the depletion layer which is experimentally observed on hydrophobic surfaces, are emphasized. For a hydrophilic sapphire surface, the authors discuss the influence of geometry and density of polar surface groups on the interfacial water structure. They discuss nonequilibrium effects arising in laminar shear flows, where the classic no-slip hydrodynamic boundary condition is violated at hydrophobic interfaces. They discuss the arising slip and relate it to static properties of the solid hydrophobic/water interface.
Collective molecular dynamics in proteins and membranes (Review)
Authors: Rheinstädter Maikel C.
Published: January 2009

The understanding of dynamics and functioning of biological membranes and, in particular, of membrane embedded proteins is one of the most fundamental problems and challenges in modern biology and biophysics. In particular, the impact of membrane composition and properties and of structure and dynamics of the surrounding hydration water on protein function is an upcoming topic, which can be addressed by modern experimental and computational techniques. Correlated molecular motions might play a crucial role for the understanding of, for instance, transport processes and elastic properties, and might be relevant for protein function. Experimentally that involves determining dispersion relations for the different molecular components, i.e., the length scale dependent excitation frequencies and relaxation rates. Only very few experimental techniques can access dynamical properties in biological materials on the nanometer scale, and resolve dynamics of lipid molecules, hydration water molecules, and proteins and the interaction between them. In this context, inelastic neutron scattering turned out to be a very powerful tool to study dynamics and interactions in biomolecular materials up to relevant nanosecond time scales and down to the nanometer length scale. The author reviews and discusses inelastic neutron scattering experiments to study membrane elasticity and protein-protein interactions of membrane embedded proteins.
Nanostructure of supported lipid bilayers in water
Authors: Nickel Bert
Published: January 2009

Biologically functional supported lipid bilayers (SLBs) used in the rising field of nanobiotechnology require fine tuning of the SLB interface with the substrate, e.g., a sensor surface. Depending on the application, membrane functionality implies a homogeneous and dense bilayer and a certain degree of diffusivity in order to allow for a rearrangement in response to, e.g., protein binding. Here, progress in the preparation, characterization, and application of SLBs obtained in the past three to five years are highlighted. Synchrotron techniques, which allow to reveal structural features within the membrane on a length scale of ∼0.5 nm are discussed in more detail, as well as the relation of structural features to dynamical membrane properties obtained by complementary optical techniques.
Nanoplasmonic biosensing with focus on short-range ordered nanoholes in thin metal films (Review)
Authors: Jonsson Magnus P. , Dahlin Andreas B. , Jönsson Peter , Höök Fredrik
Published: January 2009

The resonance conditions for excitation of propagating surface plasmons at planar metal/dielectric interfaces and localized surface plasmons associated with metal nanostructures are both sensitive to changes in the interfacial refractive index. This has made these phenomena increasingly popular as transducer principles in label-free sensing of biomolecular recognition reactions. In this article, the authors review the recent progress in the field of nanoplasmonic bioanalytical sensing in general, but set particular focus on certain unique possibilities provided by short-range ordered nanoholes in thin metal films. Although the latter structures are formed in continuous metal films, while nanoparticles are discrete entities, these two systems display striking similarities with respect to sensing capabilities, including bulk sensitivities, and the localization of the electromagnetic fields. In contrast, periodic arrays of nanoholes formed in metal films, most known for their ability to provide wavelength-tuned enhanced transmission, show more similarities with conventional propagating surface plasmon resonance. However, common for both short-range ordered and periodic nanoholes formed in metal films is that the substrate is electrically conductive. Some of the possibilities that emerge from sensor templates that are both electrically conductive and plasmon active are discussed and illustrated using recent results on synchronized nanoplasmonic and quartz crystal microbalance with dissipation monitoring of supported lipid bilayer formation and subsequent biomolecular recognition reactions. Besides the fact that this combination of techniques provides an independent measure of biomolecular structural changes, it is also shown to contribute with a general means to quantify the response from nanoplasmonic sensors in terms of bound molecular mass.