Non-invasive measurement of cholesterol in human blood by impedance technique: an investigation by 2D finite element field modelling

This paper concerns detection of solid particles suspended in conductive media by impedance technique. The technique is based on changes in impedance measured between two electrodes placed across a given volume of conducting medium. It presents a methodology for modelling and investigation of the feasibility of such a technique for particle detection by 2D finite element (FE) field modelling. This is based on modelling and computation of electric field distribution between the above electrodes. It establishes the modelling approach, the complexity involved and justifies the need for modelling in 3D to incorporate some of the effects that cannot be taken into account in 2D models. It reports on the modelling investigation for a specific case of detecting, by impedance technique cholesterol particles suspended in human blood and points to a possible instrument for non-invasive measurement of blood cholesterol level

Optical particle detection integrated in a dielectrophoretic lab-on-a-chip

The 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

Optimization of Skin Impedance Sensor Design with Finite Element Simulations

Abstract: Impedance spectroscopy is a measurement technique that has been investigated in a wide variety of medical applications. An example is the measurement of the dielectric properties of the skin and underlying tissue using sensors placed in contact with human skin with capacitive fringing field electrodes. Electrodes with different characteristic geometries measure biophysical properties at separate penetration depths in the tissue and have therefore different sensitivities to e.g. physiological processes in the tissue. When the measured depth is in the dermis layer, the time series of the measured impedance at specific frequencies can be related to the effect of glucose changes. The aim of this work is to use finite element methods (FEM) for optimizing the sensor design to maximise its sensitivity to the dielectric changes of the dermis layer. This is achieved by evaluating FEM simulations for different electrode widths and distances to ground and searching for the geometries at which the information coming from the dermis layer reach a maximum. Experimental data supports the conclusions drawn from the simulation output

Microelectrode-based dielectric spectroscopy of glucose effect on erythrocytes

The dielectric response of biconcave erythrocytes exposed to D-glucose and I.-glucose has been investigated using a double array of planar interdigitated microelectrodes on a glass microchip. Erythrocytes are analyzed under physiological conditions suspended in hypo-osmolar balanced solutions containing different glucose concentrations (0-20 mM). The glucose effect on the cellular dielectric properties is evaluated by analyzing the spectra using two different approaches, the equivalent circuit model and a modified model for ellipsoidal particles. The results show that at elevated glucose concentration (15 mM) the membrane capacitance increases by 36%, whereas the cytosol conductivity slightly decreases with a variation of about 15%. On the contrary, no variation has been registered with L-glucose, a biologically inactive enantiomer of D-glucose. The paper discusses the possible mechanism controlling the membrane dielectric response. As the external D-glucose increases, the number of activated glucose transporter in the erythrocyte membrane raises and the transition from sugar-free state to sugar-bounded state induces a change in the dipole moments and in the membrane capacitance. (C) 2011 Elsevier B.V. All rights reserved

Dielectrophoretic separation and enrichment of CD34+ cell subpopulation from bone marrow and peripheral blood stem cells

Dielectrophoresis has been used to enrich selected cell subpopulations in a mixed cell population by exploiting differential dielectric properties. Six-fold enrichment of stem cells expressing the CD34+ antigen has been achieved for bone marrow samples and peripheral blood, without the requirement for initial chemical treatment associated with immunoadsorption techniques