Chemistry of Conductive Solutions

This second chapter starts by introducing the chemical scenario where bio/CMOS interfaces usually work. In fact, it discusses the chemistry of conductive solutions. Typically, human tissues are conductive solutions based on salty water. On the one hand, the salts and other basic components of human tissues are key for the working functions of biological macromolecules. On the other hand, such samples are providing solutions that conduct electricity. This last is not necessarily a useful aspect for the bio/interfaces under development since currents provided by the sample may interfere with the signals specifically related to the desired molecular detection. Therefore, the nature of such conductive solutions is deeply discussed and characterized. The aim of this chapter is indeed to introduce the main concepts related to such a characterization, including but not limited to the concept of electrolyte, acid, base, and solution pH. The concepts of the double-layer phenomenon and Helmholtz planes are introduced as well, and the Debye length is defined. A simple and basic equivalent circuit for the electrical behavior of electrochemical interfaces between conductive solutions and electrodes of CMOS devices is also provided.