Lab-On-A-Chip Device for Yeast Cell Characterization in Low-Conductivity Media Combining Cytometry and Bio-Impedance

Abstract

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.

Flow-Through Quantification of Microplastics Using Impedance Spectroscopy

“…In flow cytometry applications, impedance spectroscopy is used to infer the electrical properties of single cells at high-throughput, − with recent results differentiating red blood cells and plastic beads at 200 cells/s . Electrodes monitor the impedance change as particles pass in a flowing medium, such as phosphate-buffered saline, ,,,, tap water, , or saltwater . Following Ohm’s law, the impedance relates a voltage source to the magnitude and phase of current passing through a circuit element as a function of frequency. ,− At low frequency, the impedance change is proportional to a particle’s volume and is used in Coulter counters for sizing. − ,− ,,, At higher frequencies, particle internal properties may be measured, such as the membrane capacitance or cytoplasm conductivity. − ,− , Impedance spectroscopy has been applied to blood analysis, , tumor cell identification, bacteria detection, and plankton discrimination .…”

“…Following Ohm’s law, the impedance relates a voltage source to the magnitude and phase of current passing through a circuit element as a function of frequency. ,− At low frequency, the impedance change is proportional to a particle’s volume and is used in Coulter counters for sizing. − ,− ,,, At higher frequencies, particle internal properties may be measured, such as the membrane capacitance or cytoplasm conductivity. − ,− , Impedance spectroscopy has been applied to blood analysis, , tumor cell identification, bacteria detection, and plankton discrimination . Plastic beads, which are used for testing and size calibration, are routinely differentiated from biological particles through a combination of high and low frequency measurements. ,,,, In impedance flow cytometry, particles are typically 1–25 μm. − ,− ,− For microplastic analysis, it is necessary to expand impedance spectroscopy to cover a larger size range (1–1000 μm) . Here, we demonstrate the utility of impedance spectroscopy for microplastic detection in tap water in the laboratory, the first step toward developing a high-throughput, in situ sensor for microplastic quantification in freshwater bodies.…”

Biosensors Based on Mechanical and Electrical Detection Techniques

“…Claudel et al have demonstrated a similar system that is sufficiently accurate to determine both the size and cytoplasm conductivity of yeast cells on the order of 3 µm. This was achieved by using differential calculations at different frequencies to distinguish between media conductivity and cytoplasm conductivity [ 176 ]. A similar design was originally used by Gawad et al to demonstrate particle sizing whilst achieving a throughput of 100 samples s −1 [ 177 ].…”

Interdigitated Sensor Optimization for Blood Sample Analysis

“…Trap sensors often use micro-hole or microcavity [ 13 ] systems to isolate cells from each other. Cytometric sensors use microchannels to focus on one cell at a time [ 14 ], and cells are dynamically characterized during their passage into a measurement area situated inside the channel. Matrix electrode systems use multiple electrodes to perform numerous measurements at a time [ 15 ].…”

“…Beyond the simple interface, the geometrical properties of the electrodes can have a significant impact on the efficiency of the biosensor [ 19 , 20 ]. They can be optimized a priori during the sensors’ design step according to the targeted application and the nature of the cells to be analyzed [ 14 ]. In this work, we propose a method for optimizing the ITD sensor frequency band involving the metalization ratio.…”