Electrodes for Cell Sensors Interfacing

In this chapter, we present a comprehensive review of the electrodes that were used, are used, or can be used for bioelectrochemical cell sensors. Such sensors are based on the functional response of living cells, e.g., microbes, yeast, mammalian cells, plant cells, etc. This chapter focuses on the electrical and bioelectrochemical response where electrodes are important components in the bioelectric and bioelectrochemical signal path. Electrodes are integrated with the micro systems to pick up the signal generated by the cells, which can be dispersed in an aqueous solution or immobilized on (or near) the electrodes. There are numerous methods for cell sensors immobilization, for example, embedding in natural polymers (e.g., agar-agar) that is deposited on the electrode, attaching to polymer beads that are attached to the electrodes, or bound to the electrodes using specific chemistry. In this chapter, we review the electrode concepts, materials, designs, and process integration methods using 2D and 3D patterning methods. We review both passive and active electrodes, discussing the role of low-impedance three-electrode configuration (e.g., working, auxiliary, and reference electrodes) as well as high-impedance capacitance and field-effect devices. The different sections are accompanied by examples demonstrating the highlights and problems in the various electrode-based whole cell biosensors.