Multiple-frequency impedance measurements in continuous flow for the evaluation of electrical lysis of yeast cells

Impedance Imaging of Cells and Tissues: Design and Applications

Due to their label-free and noninvasive nature, impedance measurements have attracted increasing interest in biological research. Advances in microfabrication and integrated-circuit technology have opened a route to using large-scale microelectrode arrays for real-time, high-spatiotemporal-resolution impedance measurements of biological samples. In this review, we discuss different methods and applications of measuring impedance for cell and tissue analysis with a focus on impedance imaging with microelectrode arrays in in vitro applications. We first introduce how electrode configurations and the frequency range of the impedance analysis determine the information that can be extracted. We then delve into relevant circuit topologies that can be used to implement impedance measurements and their characteristic features, such as resolution and data-acquisition time. Afterwards, we detail design considerations for the implementation of new impedance-imaging devices. We conclude by discussing future fields of application of impedance imaging in biomedical research, in particular applications where optical imaging is not possible, such as monitoring of ex vivo tissue slices or microelectrode-based brain implants.

Single-cell microfluidic impedance cytometry: from raw signals to cell phenotypes using data analytics

The biophysical analysis of single-cells by microfluidic impedance cytometry is emerging as a label-free and high-throughput means to stratify the heterogeneity of cellular systems based on their electrophysiology. Emerging applications range from fundamental life-science and drug assessment research to point-of-care diagnostics and precision medicine. Recently, novel chip designs and data analytic strategies are laying the foundation for multiparametric cell characterization and subpopulation distinction, which are essential to understand biological function, follow disease progression and monitor cell behaviour in microsystems. In this tutorial review, we present a comparative survey of the approaches to elucidate cellular and subcellular features from impedance cytometry data, covering the related subjects of device design, data analytics (i.e., signal processing, dielectric modelling, population clustering), and phenotyping applications. We give special emphasis to the exciting recent developments of the technique (timeframe 2017-2020) and provide our perspective on future challenges and directions. Its synergistic application with microfluidic separation, sensor science and machine learning can form an essential toolkit for label-free quantification and isolation of subpopulations to stratify heterogeneous biosystems.

New tools and new biology: recent miniaturized systems for molecular and cellular biology

Recent advances in applied physics and chemistry have led to the development of novel microfluidic systems. Microfluidic systems allow minute amounts of reagents to be processed using μm-scale channels and offer several advantages over conventional analytical devices for use in biological sciences: faster, more accurate and more reproducible analytical performance, reduced cell and reagent consumption, portability, and integration of functional components in a single chip. In this review, we introduce how microfluidics has been applied to biological sciences. We first present an overview of the fabrication of microfluidic systems and describe the distinct technologies available for biological research. We then present examples of microsystems used in biological sciences, focusing on applications in molecular and cellular biology.

Characterization of a novel impedance cytometer design and its integration with lateral focusing by dielectrophoresis

This paper reports a novel impedance cytometer design, easily integrable with dielectrophoretic focusing using a simple fabrication process with a single metal layer. Patterning of electrodes recessed in lateral channels - so-called "liquid electrodes" - allows the use of large electrodes while keeping a good spatial resolution. This larger area allows measurements at low frequencies, down to 1 kHz. It also decreases the current density, leading to electrodes more robust against electrochemical degradation. The relative change in impedance is simulated and compared to values reported in the literature for traditional designs, showing a smaller sensitivity for the proposed design due to the larger measurement volume. The device is evaluated with specific target applications, such as viability measurement and high-speed cell counting. Numerical simulations indicate that the proposed design reduces the dependence of the measurement on the vertical position of the particle compared to conventional designs, with a variation of only 5%, but is still dependent on its lateral position. This dependence is studied using focusing by dielectrophoresis (DEP) at different lateral positions across the microchannel, showing a larger sensitivity when the particles are close to the measurement electrodes, as confirmed by the numerical simulations. The integration of lateral dielectrophoresis to focus particles in the middle of the channel reduces the variation of the measurements to very small values, with a coefficient of variation of 5.6%, and allows precise particle sizing. Such a design can be very powerful to simplify the fabrication process of impedance cytometers and enables the production of cost-effective, possibly disposable devices.