| 1. |
- Bernander, Stig, et al.
(författare)
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Downhill progressive landslides in long natural slopes: triggering agents and landslide phases modeled with a finite difference method
- 2016
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Ingår i: Canadian geotechnical journal (Print). - : Canadian Science Publishing. - 0008-3674 .- 1208-6010. ; 53:10, s. 1565-1582
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Tidskriftsartikel (refereegranskat)abstract
- A large landslide in Tuve (Gothenburg, Sweden 1977) initiated the development of a model for slope stability analysis taking the deformation-softening of soft sensitive clays into consideration. The model studies triggering agents and five phases in progressive slope failure are identified: (1) in-situ, (2) disturbance, (3) unstable ‘dynamic’, (4) transitory (or permanent) equilibrium, and (5) ‘global’ failure. The clay resistance in these phases may differ widely; mostly due to different rates of loading. Two time dependent failure criteria are defined: (i) the triggering load condition in the disturbance Phase (2), and (ii) the transitory equilibrium in Phase (4), indicating whether minor downhill displacements or a veritable landslide catastrophe will occur. The analysis explains why downhill landslides tend to spread over vast areas of almost horizontal ground further down-slope. The model has been applied to landslides in Scandinavia and Canada. Three case studies are briefly discussed. The model is a finite difference approach, where local downhill deformations caused by normal forces is maintained compatible with deviatory shear deformations above the potential (or the established) failure surface. Software and an easy-to-use spreadsheet are introduced as well as recent developments. See also Video Abstract.
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| 2. |
- Jansson, Erik, 1984, et al.
(författare)
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Microfluidic Flow Cell for Sequential Digestion of Immobilized Proteoliposomes
- 2012
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 84:13, s. 5582-5588
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a microfluidic flow cell where stepwise enzymatic digestion is performed on immobilized proteoliposomes and the resulting cleaved peptides are analyzed with liquid chromatography–tandem mass spectrometry (LC–MS/MS). The flow cell channels consist of two parallel gold surfaces mounted face to face with a thin spacer and feature an inlet and an outlet port. Proteoliposomes (50–150 nm in diameter) obtained from red blood cells (RBC), or Chinese hamster ovary (CHO) cells, were immobilized on the inside of the flow cell channel, thus forming a stationary phase of proteoliposomes. The rate of proteoliposome immobilization was determined using a quartz crystal microbalance with dissipation monitoring (QCM-D) which showed that 95% of the proteoliposomes bind within 5 min. The flow cell was found to bind a maximum of 1 μg proteoliposomes/cm2, and a minimum proteoliposome concentration required for saturation of the flow cell was determined to be 500 μg/mL. Atomic force microscopy (AFM) studies showed an even distribution of immobilized proteoliposomes on the surface. The liquid encapsulated between the surfaces has a large surface-to-volume ratio, providing rapid material transfer rates between the liquid phase and the stationary phase. We characterized the hydrodynamic properties of the flow cell, and the force acting on the proteoliposomes during flow cell operation was estimated to be in the range of 0.1–1 pN, too small to cause any proteoliposome deformation or rupture. A sequential proteolytic protocol, repeatedly exposing proteoliposomes to a digestive enzyme, trypsin, was developed and compared with a single-digest protocol. The sequential protocol was found to detect 65% more unique membrane-associated protein (p
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| 3. |
- Lobovkina, Tatsiana, 1975, et al.
(författare)
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Protrusive growth and periodic contractile motion in surface-adhered vesicles induced by Ca2+-gradients
- 2010
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 6:2, s. 268-272
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Tidskriftsartikel (refereegranskat)abstract
- Local signaling, cell polarization, and protrusive growth are key steps in directed migration of biological cells guided by chemical gradients. Here we present a minimal system which captures several key features of cellular migration from signaling-to-motion. The model system consists of flat, negatively charged phospholipid vesicles, a negatively charged surface, and a local, and controllable point-source supply of calcium ions. In the presence of a Ca2+ gradient, the surface-adhered vesicles form protrusions in the direction of the gradient. We also observe membrane shape oscillations between expanded (flattened), and spherical states as a function of the Ca2+-concentration. The observed phenomena can be of importance in explaining motile action in prebiotic, primitive, and biomimetic systems, as well as in development of novel soft-matter nano-and microscale mechanical devices.
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| 4. |
- Olofsson, Jessica, 1975, et al.
(författare)
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A microfluidics approach to the problem of creating separate solution environments accessible from macroscopic volumes
- 2004
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 76:17, s. 4968-4976
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Tidskriftsartikel (refereegranskat)abstract
- We report on a microfluidic device that generates separate solution environments in macroscopic volumes. Spatially distinct patterns are created by emitting fluids from 16 different sources (closely spaced microchannels) into a solution-filled macroscopic chamber. The fluid in neighboring microchannels couples viscously in the macroscopic container, generating one single interdigitated stream. Scanning nanoelectrode amperometry was used for characterizing the concentration landscape and the diffusion zones between solutions running in parallel at different coordinates in the stream. These experiments were complemented by finite element simulations of the Navier-Stokes and mass transport equations to describe the velocity distributions and the diffusion behavior. For in channel flow velocities of 50 mm·s -1 , patterns could persist on the order of millimeters to centimeters in the open volume. The most narrow diffusion zones with widths less than 10 μm (5-95% concentration change) were found some tens of micrometers out in the macroscopic container. We demonstrate that a 14-μm-diameter nearly spherical object (biological cell) attached to a micropipet can be moved from one solution environment to another by a lateral displacement of only 8 μm. The device is suitable for applications where the solution environment around a microscopic or nanoscopic sensor needs to be changed multiple times, i.e., in order to build layered structures, for obtaining binding isotherms, and kinetic information, for example, on ion channels, enzymes, and receptors as well as in applications where different loci on an object need to be exposed to different environments or where complex solution environments need to be created for studies of interfacial chemistry between two streaming layers.
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| 5. |
- Pihl, Johan, 1975, et al.
(författare)
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Microfluidic gradient-generating device for pharmacological profiling
- 2005
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 77:13, s. 3897-3903
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Tidskriftsartikel (refereegranskat)abstract
- We describe an on-chip microfluidic gradient-generating device that generates concentration gradients spanning nearly 5 orders of magnitude starting from a single concentration. The exiting stream of drugs held at different concentrations remains laminar in a recording chamber and can be presented as 24 discrete solutions to a cell-based sensor. The high-performance characteristics of the device are demonstrated by pharmacological screening of voltage-gated K + channels (hERG) and ligand-gated GABAA receptors using scanning-probe patch-clamp measurements. Multiple data point dose-response curves and IC 50 and EC 50 values were rapidly obtained, typically in less than 30 min, through its combined functionality of gradient generation and open-volume laminar flow. The device facilitates rapid pharmacological profiling of ion channel and GPCR effectors and enables the acquisition of large numbers of data points with minute sample consumption and handling. © 2005 American Chemical Society.
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| 6. |
- Agarwal, A., et al.
(författare)
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Control of the Release of Freely Diffusing Molecules in Single-Cell Electroporation
- 2009
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 81:19, s. 8001-8008
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Tidskriftsartikel (refereegranskat)abstract
- Single-cell electroporation using an electrolyte-filled capillary is an emerging technique for transient pore formation in adherent cells. Because adherent cells do not have a simple and consistent shape and because the electric field emanating from the tip of the capillary is inhomogeneous, the Schwan equation based on spherical cells in homogeneous electrical fields does not apply. We sought to determine experimental and cell parameters that influence the outcome of a single-cell electroporation experiment. A549 cells were exposed to the thiol-reactive dye Thioglo-1, leading to green fluorescence from intracellular thiol adducts. Electroporation causes a decrease with time of the intracellular fluorescence intensity of Thioglo-1-loaded cells from diffusive loss of thiol adducts. The transient curves thus obtained are well-described by a simple model originally developed by Puc et al. We find that the final fluorescence following electroporation is related to the capillary tip-to-cell distance and cell size (specifically, 2(A/pi)(1/2) where A is the area of the cell's image in pixels. This quantity is the diameter if the image is a circle). In separate experiments, the relationship obtained can be used to control the final fluorescence following electroporation by adjusting the tip-to-cell distance based on cell size. The relationship was applied successfully to A549 as Well as DU 145 and PC-3 cells. Finally, F-tests show that the variability in the final fluorescence (following electroporation) is decreased when the tip-to-cell distance is controlled according to the derived relationship in comparison to experiments in which the tip-cell distance is a constant irrespective of cell size.
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| 7. |
- Agarwal, A., et al.
(författare)
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Effect of cell size and shape on single-cell electroporation
- 2007
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 79:10, s. 3589-3596
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Tidskriftsartikel (refereegranskat)abstract
- Single-cell electroporation was performed using electrolyte-filled capillaries on fluorescently labeled A549 cells. Cells were exposed to brief pulses (50-300 ms) at various cell-capillary tip distances. Cell viability and electroporation success were measured. In order to understand the variability in single-cell electroporation, logistic regression was used to determine whether the probabilities of cell survival and electroporation depend on experimental conditions and cell properties. Both experimental conditions and cell properties (size and shape) have a significant effect on the outcome. Finite element simulations were used to compare bulk electroporation to single-cell electroporation in terms of cell size and shape. Cells are more readily permeabilized and are more likely to survive if they are large and hemispherical as opposed to small and ellipsoidal with a high aspect ratio. The dependence of the maximum transmembrane potential across the cell membrane on cell size is much weaker than it is for bulk electroporation. Observed survival probabilities are related to the calculated fraction of the cell's surface area that is electroporated. Observed success of electroporation is related to the maximum transmembrane potential achieved.
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| 8. |
- Bell, Brian, et al.
(författare)
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Sustainable Bridges - Past and Future Reflections on a European Project 2003-2007
- 2023
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Ingår i: IABSE Congress, New Delhi 2023: Engineering for Sustainable Development, Report. ; , s. 690-698
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Konferensbidrag (refereegranskat)abstract
- Twenty years ago, in 2003, a European project was started to increase the sustainability of existing railway bridges. This paper summarises what was achieved and looks ahead. Nine Working Packages were organized: (1) Background material; (2) Guidance by stakeholders; (3) Condition Assessment and Inspection Guidelines; (4) Loads, Capacity and Resistance Guidelines; (5) Monitoring Guidelines; (6) Repair and Strengthening Guidelines; (7) Demonstration with Field testing of Bridges; (8) Demonstration on Monitoring on Bridges; and (9) Training and Dissemination Some of the main results (from 4 Guidelines and 47 Background documents) are highlighted and some experiences, conclusions and thoughts about the future are given. Hidden strengths and weaknesses are discussed, analyses and codes for assessment can be improved, new monitoring and strengthening methods are available and life length can be prolonged.
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| 9. |
- Bridle, Helen, 1979, et al.
(författare)
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Automated control of local solution environments in open-volume microfluidics
- 2007
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 79:24, s. 9286-9293
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Tidskriftsartikel (refereegranskat)abstract
- We present an open-volume microfluidic system capable of on-fine modification of a patterned laminar flow by using programmable inlet valves. Each separate solution environment in the flow pattern can be independently exchanged between different preloaded input solutions where each exchange requires 20 s. The number of flow patterns that can be generated by one device is N-n, where N represents the number of valve inlets and n the number of microchannels in the microfluidic system. Furthermore, the system can be operated as a combinatorial mixer, in which mixture of the different input solutions can be obtained independently in each channel. Since the flow patterns are generated in an open volume, they are accessible to many different detection methods and types of probes, e.g., microelectrodes, cells, or cell fragments. This technology offers the possibility to adjust the flow pattern composition in response to an output from a probe. This is the first step toward creating an automated feedback device controlled by, for example, biological cells.
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| 10. |
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| 11. |
- Lambie, B. A., et al.
(författare)
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Experimentally determining the iR drop in solution at carbon fiber microelectrodes with current interruption and application to single-cell electroporation
- 2007
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 79:10, s. 3771-3778
-
Tidskriftsartikel (refereegranskat)abstract
- Single-cell electroporation uses microelectrodes, capillaries, or micropipets positioned near single, adherent cells to increase transiently the membrane permeability of the cell. The increased permeability permits, for example, transfection without chemical reagents. When using microelectrodes to apply an electric field to the cell, there is a question of how much voltage to apply. Unlike in bulk electroporation, where hundreds of volts may be applied between electrodes, a rather small voltage is applied to a microelectrode in single-cell electroporation. In the single-cell experiment with microelectrodes, a substantial fraction of the voltage is lost at the interface and does not therefore exist in solution. This problem is the same as the classical electrochemist's problem of knowing the "iR" drop in solution and correcting for it to obtain true interfacial potential differences. Therefore, we have used current interruption to determine the iR drop in solution near microcylinder electrodes. As the field is inhomogeneous, calculations are required to understand the field distribution. Results of the current interruption are validated by comparing two independent measurements of the resistance in solution: one value results from the measured iR drop in conjunction with the known applied current. The other value results from a measured solution conductivity and a computed cell constant. We find substantial agreement in the range of resistances from about 2 to 50 k Omega, but not at higher resistances. We propose a simple, four-step plan that takes a few minutes to calculate the approximate current required to electroporate a cell with an electrode of a particular size, shape, and distance from the cell. We validate the approach with electroporation of single A549 cells.
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| 12. |
- Olofsson, Jessica, 1975, et al.
(författare)
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A chemical waveform synthesizer
- 2005
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Ingår i: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 102:23, s. 8097-8102
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Tidskriftsartikel (refereegranskat)abstract
- Algorithms and methods were developed to synthesize complex chemical waveforms in open volumes by using a scanning-probe microfluidic platform. Time-dependent variations and oscillations of one or several chemical species around the scanning probe, such as formation of sine waves, damped oscillations, and generation of more complex patterns, are demonstrated. Furthermore, we show that intricate bursting and chaotic calcium oscillations found in biological microdomains can be reproduced and that a biological cell can be used as a probe to study receptor functionalities as a function of exposure to time-dependent variations of receptor activators and inhibitors. Thus, the method allows for studies of biologically important oscillatory reactions. More generally, the system allows for detailed studies of complex time-varying chemical and physical phenomena in solution or at solution/surface interfaces.
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| 13. |
- Olofsson, Jessica, 1975
(författare)
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A Solution Exchange Platform for Exposure of Cells to Chemical Waves
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents the development, characterization and suggested applications of a platform for controlling the chemical environment around a cell or a cell constituent. The platform is unique in its capability to combine rapid solution switching with precise timing and access to a manifold of solution environments. It can be used to present a sequence of different solution environments to a cell or cell constituent, with rapid switching between them. Furthermore, the system can be used to expose cells and their constituents to complex chemical waves and oscillations, either mimicking concentration variations found in vivo, or of artificially composed patterns. The system comprises a microfluidic device and a motorized computer-controlled scanning stage that has micrometer precision. The device contains a varied number of channels which start in individual sample reservoirs and exit as a closely packed array into an open volume. By loading the sample reservoirs with different solutions, a stripe-patterned flow can be formed outside the channel exits. If a cell is scanned in this patterned flow, its chemical environment can be controlled and varied with high precision.The platform can be used for applications in ion channel research and drug discovery. To confirm this, it was combined with standard patch-clamp equipment, and rapid generation of dose-response curves and sequential stimulation of an ion channel population with different kinds of agonists were demonstrated. Additional possible applications of the system range from elucidation of signalling network properties, to experiments on decoding of temporal signalling patterns that are used by cells. To characterize the stripe-patterned fluid flow, and the diffusion-driven mixing of species within it, fluorescence microscopy and scanning nanoelectrode amperometry were used. The fluid flow and the diffusion of species were modelled with the finite element method, implemented using the commercial software FEMLAB.
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| 14. |
- Olofsson, Jessica, 1975, et al.
(författare)
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Direct Access and Control of the Intracellular Solution Environment in Single Cells
- 2009
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 81:5, s. 1810-1818
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Tidskriftsartikel (refereegranskat)abstract
- Methods that can control and vary the solution environment around single cells are abundant. In contrast, methods that offer direct access to the intracellular proteome and genome in single cells with the control, flexibility, and convenience given by microfluidic methods are both scarce and in great demand. Here, we present such a method based on using a microfluidic device mounted on a programmable scanning stage and cells on-chip permeabilized by the pore-forming glycoside digitonin. We characterized the on-chip digitonin poration, as well as the solution exchange within cells. Intracellular solution exchange times vary with the dose of exposure to digitonin from less than a second to tens of seconds. Also, the degree of permeabilization obtained for cells treated with the same dose varies considerably, especially for low doses of digitonin exposure and low permeabilities. With the use of the presented setup, the degree of permeabilization can be measured during the permeabilization process, which allows for "on-line" optimization of the digitonin exposure time. Using this calibrated permeabilization method, we demonstrate the generation of intracellular oscillations, intracellular gradients, and the delivery of substrate to initiate enzymatic reactions in situ. This method holds the potential to screen and titrate intracellular receptors or enzymes or to generate intracellular oscillations, useful in the study of signaling pathways and oscillation decoding among other applications.
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| 15. |
- Olofsson, Jessica, 1975, et al.
(författare)
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Generation of focused electric field patterns at dielectric surfaces
- 2005
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 77:14, s. 4667-4672
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Tidskriftsartikel (refereegranskat)abstract
- We here report on a concept for creating well-defined electric field gradients between the boundaries of capillary electrode (a capillary of a nonconducting material equipped with an interior metal electrode) outlets, and dielectric surfaces. By keeping a capillary electrode opening close to a boundary between a conducting solution and a nonconducting medium, a high electric field can be created close to the interface by field focusing effects. By varying the inner and outer diameters of the capillary, the span of electric field strengths and the field gradient obtained can be controlled, and by varying the slit height between the capillary rim and the surface, or the applied current, the average field strength and gradient can be varied. Field focusing effects and generation of electric field patterns were analyzed using finite element method simulations. We experimentally verified the method by electroporation of a fluorescent dye (fluorescein diphosphate) into adherent, monolayered cells (PC-12 and WSS-1) and obtained a pattern of fluorescent cells corresponding to the focused electric field.
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| 16. |
- Olofsson, Jessica, 1975, et al.
(författare)
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Probing enzymatic activity inside single cells.
- 2013
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 85:21, s. 10126-33
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Tidskriftsartikel (refereegranskat)abstract
- We report a novel approach for determining the enzymatic activity within a single suspended cell. Using a steady-state microfluidic delivery device and timed exposure to the pore-forming agent digitonin, we controlled the plasma membrane permeation of individual NG108-15 cells. Mildly permeabilized cells (∼100 pores) were exposed to a series of concentrations of fluorescein diphosphate (FDP), a fluorogenic alkaline phosphatase substrate, with and without levamisole, an alkaline phosphatase inhibitor. We generated quantitative estimates for intracellular enzyme activity and were able to construct both dose-response and dose-inhibition curves at the single-cell level, resulting in an apparent Michaelis contant Km of 15.3 μM ± 1.02 (mean ± standard error of the mean (SEM), n = 16) and an inhibition constant Ki of 0.59 mM ± 0.07 (mean ± SEM, n = 14). Enzymatic activity could be monitored just 40 s after permeabilization, and five point dose-inhibition curves could be obtained within 150 s. This rapid approach offers a new methodology for characterizing enzyme activity within single cells.
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| 17. |
- Olofsson, Jessica, 1975, et al.
(författare)
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Scanning electroporation of selected areas of adherent cell cultures
- 2007
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 79:12, s. 4410-4418
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Tidskriftsartikel (refereegranskat)abstract
- We present a computer-controlled scanning electroporation method. Adherent cells are electroporated using an electrolyte-filled capillary in contact with an electrode. The capillary can be scanned over a cell culture and locally deliver both an electric field and an electroporation agent to the target area without affecting surrounding cells. The instantaneous size of the targeted area is determined by the dimensions of the capillary. The size and shape of the total electroporated area are defined by these dimensions in combination with the scanning pattern. For example, striped and serpentine patterns of electroporated cells in confluent cultures can be formed. As it is easy to switch between different electroporation agents, the method is suitable for design of cell cultures with complex composition. Finite element method simulations were used to study the spatial distributions of the electric field and the concentration of an electroporation agent, as well as the fluid dynamics related to scanning and flow of electroporation agent from the capillary. The method was validated for transfection by introduction of a 9-base-pair-long randomized oligonucleotide into PC12 cells and a pmaxGFP plasmid coding for green fluorescent protein into CHO and WSS cells.
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| 18. |
- Tokarz, Michal, 1976, et al.
(författare)
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Single-file electrophoretic transport and counting of individual DNA molecules in surfactant nanotubes
- 2005
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 102:26, s. 9127-9132
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a complete nanotube electrophoresis system (nanotube radii in the range of 50 to 150 nm) based on lipid membranes, comprising DNA injection, single-molecule transport, and single-molecule detection. Using gel-capped electrodes, electrophoretic single-file transport of fluorescently labeled dsDNA molecules is observed inside nanotubes. The strong confinement to a channel of molecular dimensions ensures a detection efficiency close to unity and identification of DNA size from its linear relation to the integrated peak intensity. In addition to constituting a nanotechnological device for identification and quantification of single macromolecules or biopolymers, this system provides a method to study their conformational dynamics, reaction kinetics, and transport in cell-like environments.
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| 19. |
- Wang, M. Y., et al.
(författare)
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Single-cell electroporation
- 2010
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Ingår i: Analytical and Bioanalytical Chemistry. - : Springer Science and Business Media LLC. - 1618-2642 .- 1618-2650. ; 397:8, s. 3235-3248
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Tidskriftsartikel (refereegranskat)abstract
- Single-cell electroporation (SCEP) is a relatively new technique that has emerged in the last decade or so for single-cell studies. When a large enough electric field is applied to a single cell, transient nano-pores form in the cell membrane allowing molecules to be transported into and out of the cell. Unlike bulk electroporation, in which a homogenous electric field is applied to a suspension of cells, in SCEP an electric field is created locally near a single cell. Today, single-cell-level studies are at the frontier of biochemical research, and SCEP is a promising tool in such studies. In this review, we discuss pore formation based on theoretical and experimental approaches. Current SCEP techniques using microelectrodes, micropipettes, electrolyte-filled capillaries, and microfabricated devices are all thoroughly discussed for adherent and suspended cells. SCEP has been applied in in-vivo and in-vitro studies for delivery of cell-impermeant molecules such as drugs, DNA, and siRNA, and for morphological observations.
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