478 research outputs found
Electrokinetic measurements of membrane capacitance and conductance for pancreatic -cells
No full textAuthor Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of IEE for personal use, not for redistribution. The definitive version was published in IEE Proceedings - Nanobiotechnology 152 (2005): 189-193, doi:10.1049/ip-nbt:20050040.Membrane capacitance and membrane conductance values are reported for insulin secreting cells (primary β-cells and INS-1 insulinoma cells) determined using the methods of dielectrophoresis and electrorotation. The membrane capacitance value of 12.57 (± 1.46) mF/m2 obtained for β-cells, and the values 9.96 (± 1.89) mF/m2 to 10.65 (± 2.1) mF/m2 obtained for INS-1 cells, fall within the range expected for mammalian cells. The electrorotation results for the INS-1 cells lead to a value of 36 (± 22) S/m2 for the membrane conductance associated with ion channels, if values in the range 2nS to 3 nS are assumed for the membrane surface conductance. This membrane conductance value falls within the range reported for INS cells obtained using the whole-cell patch-clamp technique. However, the total ‘effective’ membrane conductance value of 601 (± 182) S/m2 obtained for the INS-1 cells by dielectrophoresis is significantly larger (by a factor of around three-fold) than the values obtained by electrorotation. This could result from an increased membrane surface conductance, or increased passive conduction of ions through membrane pores, induced by the larger electric field stresses experienced by cells in the dielectrophoresis experiments.This study was financed by a gift from the Denis Robinson Memorial Fund to RP and NIH grants NCRR RR001395 and DK06984 to PJSS
Nonlinear Production, Abatement, Pollution and Materials Balance Reconsidered
No full textIn the environmental economics literature the standard approach of modeling nonlinear production and abatement processes is to treat waste emissions "simply as another factor of production" (Cropper and Oates 1992). That approach doesn't map the materials flow involved completely and hides, moreover, the exact links between production, residuals generation and abatement. This paper shows that production functions with emissions treated as inputs can be reconstructed as a subsystem of a comprehensive production-cum-abatement technology that is in line with the materials-balance principle. In a simple economy with full regard of the materials flow it also explores the consequences for allocative efficiency and efficiency-restoring taxation of multiple and interdependent residuals generated in the transformation processes of production, abatement and consumption. Finally, the paper demonstrates that efficiency may require setting the emissions tax rate above or below conventionally defined marginal abatement cost if the residual subject to abatement is not the only residual causing pollution.residuals, abatement, pollution, materials balance
Dielectrophoretic tweezer for isolating and manipulating target cells
No full textThe ability to isolate and accurately position single cells in three dimensions is becoming increasingly important in many areas of biological research. The authors describe the design, theoretical modelling and testing of a novel dielectrophoretic (DEP) tweezer for picking out and relocating single target cells. The device is constructed using facilities available in most electrophysiology laboratories, without the requirement of sophisticated and expensive microfabrication technology, and offers improved practical features over previously reported DEP tweezer designs. The DEP tweezer has been tested using transfected HEI-193 human schwannoma cells, with visual identification of the target cells being aided by labelling the incorporated gene product with a green fluorescent protei
Dielectrophoretic assembly of insulinoma cells and fluorescent nanosensors into three-dimensional pseudo-islet constructs
No full textDielectrophoretic forces, generated by radio-frequency voltages applied to micromachined, transparent, indium tin oxide electrodes, have been used to condense suspensions of insulinoma cells (BETA-TC-6 and INS-1) into a 10times10 array of three-dimensional cell constructs. Some of these constructs, measuring ~150 mum in diameter, 120 mum in height and containing around 1000 cells, were of the same size and cell density as a typical islet of Langerhans. With the dielectrophoretic force maintained, these engineered cell constructs were able to withstand mechanical shock and fluid flow forces. Reproducibility of the process required knowledge of cellular dielectric properties, in terms of membrane capacitance and membrane conductance, which were obtained by electrorotation measurements. The ability to incorporate fluorescent nanosensors, as probes of cellular oxygen and pH levels, into these 'pseudo-islets' was also demonstrated. The footprint of the 10times10 array of cell constructs was compatible with that of a 1536 microtitre plate, and thus amenable to optical interrogation using automated plate reading equipment
Dielectrophoretic investigations of internal cell properties
No full textDielectrophoresis (DEP) is a term which describes the motion of polarisable particles
induced by a non-uniform electric field. It has been the subject of research into a variety of
fields including nanoassembly, particle filtration and biomedicine. The application of DEP to
the latter has gained significant interest in recent years, driven by the development of
microfluidic “Lab-on-a-chip” devices designed to perform sophisticated biochemical
processes. It provides the ability to characterise and selectively manipulate cells based on
their distinct dielectric properties in a manner which is non-invasive and label free, by using
electrodes which can be readily integrated with microfluidic channels.
Under appropriate conditions a biological cell will experience a DEP force directing it either
towards or away from concentrations in the electric field. At a so-called “crossover
frequency” the cell is effectively invisible to the field resulting in no DEP force, a response
typically observed in the 1 kHz to 1 MHz range. Its value is a function of cell membrane
dielectric properties and has been the subject of research directed at devices capable of using
it to both characterise and sort cells.
The aim of this work was to investigate the behaviour of a higher frequency crossover
referred to as fxo2, predicted to occur in the 1 MHz to 1 GHz range. At these frequencies the
electric field is expected to penetrate the cell membrane and behave as a function of
intracellular dielectric properties. Standard lithography techniques have been used to
fabricate electrodes carefully designed to operate at these frequencies. The existence of fxo2
was then confirmed in murine myeloma cells, in good agreement with dielectric models
derived from impedance spectroscopy. A temperature dependent decrease in its value was
observed with respect to the time that cells were suspended in a DEP solution. This decrease
is consistent with previous studies which indicated an efflux of intracellular ions under
similar conditions.
An analytical derivation of fxo2 demonstrates its direct proportionality to intracellular
conductivity. Direct control of the crossover was achieved by using osmotic stress to dilute
the intracellular compartment and thereby alter its conductivity. By using a fluorophore
which selectively binds to potassium, a strong relationship has been demonstrated between
the value of fxo2 and the concentration of intracellular potassium. Measurements of fxo2 for an
unfed culture demonstrated a correlation with viability and subtle shifts in its distribution
were caused by the early stages of chemically induced apoptosis
Numerical simulation of travelling wave induced electrothermal fluid flow
No full textMany microdevices for manipulating particles and cells use electric fields to produce a motive force on the particles. The movement of particles in non-uniform electric fields is called dielectrophoresis, and the usual method of applying this effect is to pass the particle suspension over a microelectrode structure. If the suspension has a noticeable conductivity, one important side effect is that the electric field drives a substantial conduction current through the fluid, causing localized Joule-heating. The resulting thermal gradient produces local conductivity and permittivity changes in the fluid. dielectrophoretic forces acting upon these pockets of fluid will then produce motion of both the fluid and the particles. This paper presents a numerical solution of the electrical force and the resulting electrothermal driven fluid flow on a travelling wave structure. This common electrode geometry consists of interdigitated electrodes laid down in a long array, with the phase of the applied potential shifted by 90° on each subsequent electrode. The resulting travelling electric field was simulated and the thermal field and electrical body force on the fluid calculated, for devices constructed from two typical materials: silicon and glass. The electrothermal fluid flow in the electrolyte over the electrode array was then numerically simulated. The model predicts that the thermal field depends on the conductivity and applied voltage, but more importantly on the geometry of the system and the material used in the construction of the device. The velocity of the fluid flow depends critically on the same parameters, with slight differences in the thermal field for glass and silicon leading to diametrically opposite flow direction with respect to the travelling field for the two materials. In addition, the imposition of slight external temperature gradients is shown to have a large effect on the fluid flow in the device, under certain conditions leading to a reversal of the fluid flow direction
Dielectrophoresis: A Review of Applications for Stem Cell Research
No full textDielectrophoresis can discriminate distinct cellular identities in heterogeneous populations, and monitor cell state changes associated with activation and clonal expansion, apoptosis, and necrosis, without the need for biochemical labels. Demonstrated capabilities include the enrichment of haematopoetic stem cells from bone marrow and peripheral blood, and adult stem cells from adipose tissue. Recent research suggests that this technique can predict the ultimate fate of neural stem cells after differentiation before the appearance of specific cell-surface proteins. This review summarises the properties of cells that contribute to their dielectrophoretic behaviour, and their relevance to stem cell research and translational applications.</p
Pricing the Ecosystem and Taxing Ecosystem Services: A General Equilibrium Approach
No full textIn an integrated dynamic general equilibrium model of the economy and the ecosystem humans and wildlife species compete for land and prey biomass. We introduce a competitive allocation mechanism in both submodels such that economic prices and ecosystem prices guide the allocation in the economy and in the ecosystem, respectively. We distinguish the scenarios of an open accessible habitat and a privately owned habitat. In both scenarios efficiency requires different corrective taxes/subsidies to internalize consumption services externalities. In the case of an open access habitat additional sources of inefficiency are the divergence of prices for biomass and land in both subsystems. Finally, we determine values of all components of the ecosystem in an efficient steady state with special emphasis on the role and the interplay of ecosystem and economic prices.land, biomass, ecosystem services
Optical particle detection integrated in a dielectrophoretic lab-on-a-chip
No full textThe design and fabrication of a dielectrophoretic "lab-on-a-chip" device for bioparticle processing and counting is presented. The device consists of a multi-layer travelling wave dielectrophoretic electrode array for manipulating particles and/or fluids, micro channels for delivering samples, and optical fibres for counting particles and/or measuring their velocities. Single particles were detected optically using either light scattering or fluorescence emission. The technology described in this work is potentially applicable to a range of particulate diagnostic systems
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