This paper is concerned with a physical model of an interdigitated sensor working in a frequency range from 100 Hz to 10 MHz. A theoretical approach is proposed to optimize the use of the sensor for bioimpedance spectroscopy. The correlation between design parameters and frequency behavior in coplanar impedance sensors are described. CoventorWare  software was used to model the biological medium loaded interdigital sensor in three dimensions to measure its electrical impedance. Complete system simulation by a finite element method (FEM) was used for sensor sensitivity optimization. The influence of geometrical parameters (number of fingers, width of the electrodes) on the impedance spectroscopy of the biological medium was studied. The simulation results are in agreement with the theoretical equations of optimization. Thus, it is possible to design a priori such sensor by taking into account the biological medium of interest that will load the sensor.

We present an efficient and high-sensitive thermal micro-sensor for near wall flow parameters measurements. By combining substrate-free wire structure and mechanical support using silicon oxide micro-bridges, the sensor achieves a high temperature gradient, with wires reaching 1 mm long for only 3 lm wide over a 20 lm deep cavity. Elaborated to reach a compromise solution between conventional hot-films and hot-wire sensors, the sensor presents a high sensitivity to the wall shear stress and to the flow direction. The sensor can be mounted flush to the wall for research studies such as turbulence and near wall shear flow analysis, and for technical applications, such as flow control and separation detection. The fabrication process is CMOS-compatible and allows on-chip integration. The present letter describes the sensor elaboration, design, and microfabrication, then the electrical and thermal characterizations, and finally the calibration experiments in a turbulent boundary layer wind tunnel.

This paper presents an optimization of a single cell electrical model, based on Maxwell's mixture Theory, applied to flow cytometry coupled to impedance spectroscopy. It is based on the discretization of the measurement area into a square reference volume, centered between microelectrodes, and fixed impedance areas. The first one represents the sensing area, the one impacted by cell presence during measurement, and the second one, all other areas that contribute to global measured impedance. By removing these last impedances, it is possible to compare and model the electrical response of different electrodes geometries. Simulations, performed for 6 different electrodes geometries using Finite Element Method (FEM), were performed to check our assumptions. Results attest the validity of our model for cells with sizes comprised between 30 and 70% of the channel weigh. Finally, measurements performed with our microfluidic sensor show the same impedance variation distribution during the passage of calibrated beads with an error lower than 5%.

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This paper proposes a simple approach to optimize the operating frequency band of a lab-on-a-chip based on bio-impedance cytometry for a single cell. It mainly concerns applications in low-conductivity media. Bio-impedance allows for the characterization of low cell concentration or single cells by providing an electrical signature. Thus, it may be necessary to perform impedance measurements up to several tens of megahertz in order to extract the internal cell signature. In the case of single cells, characterization is performed in a very small volume down to 1 pL. At the same time, measured impedances increase from tens of kilo-ohms for physiological liquids up to several mega-ohms for low conductivity media. This is, for example, the case for water analysis. At frequencies above hundreds of kilohertz, parasitic effects, such as coupling capacitances, can prevail over the impedance of the sample and completely short-circuit measurements. To optimize the sensor under these conditions, a complete model of a cytometry device was developed, including parasitic coupling capacitances of the sensor to take into account all the impedances. It appears that it is possible to increase the pass band by optimizing track geometries and placement without changing the sensing area. This assumption was obtained by measuring and comparing electrical properties of yeast cells in a low-conductivity medium (tap water). Decreased coupling capacitance by a factor higher than 10 was obtained compared with a previous non-optimized sensor, which allowed for the impedance measurement of all electrical properties of cells as small as yeast cells in a low-conductivity medium.

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Bioimpedance spectroscopy is a promising tool for non-invasive monitoring of tissue structure and fluids. With the objective of using it to assess muscle fatigue in vitro, we have developed a measurement bench allowing the monitoring of myoblasts cultures by bioimpedance measurements. This work presents the setup and its characterization, combining modeling and measurements. This setup relies on a microelectrodes array and a commercial impedance analyzer. Its characterization with Phosphate Buffered Saline is coherent with our simulation. The impedance increases at low frequencies after several cell cultures, due to a degradation of the microelectrode interface. Nevertheless, the measurement bench allows us to detect the presence of myoblasts covering the electrodes in a frequency range from 10 kHz to 100 kHz. The measurement bench is therefore suitable to explore the relative impedance variation as a signature of muscle fatigue.