Electrochemical sensing devices constitute one of the largest groups of bio/chemical sensing devices, together with optical sensing devices. Electrochemical sensing principles can be broadly categorized into amperometry, voltammetry, potentiometry, and impedimetry. For amperometry and voltammetry, three-electrode systems consisting of working, reference, and auxiliary electrodes are typically employed. The potential of the working electrode is fixed (for amperometry) or varied (for voltammetry), and the current generated as a result of the electrode reactions is measured. To detect the progress of redox reactions, bipolar electrochemistry features the use of electrically isolated electrodes and the output is typically provided by electrochemiluminescence. Potentiometry is typically conducted for ion sensing using a two-electrode configuration consisting of an ion-selective electrode (ISE) and reference electrode. The potential of the ISE can be correlated with the analyte concentration following the Nernst equation or Nikolskii–Eisenman equation. In impedimetry, changes in the impedance at the electrode/solution interface are primarily measured, which is correlated with the progress of events that occur at the interface. Biosensors to detect analytes such as small molecules, DNA, proteins, and cells can be created by coupling chemical changes caused by receptor molecules such as enzymes, DNA, and antibodies with the aforementioned techniques. Enzyme reaction products or binding of analyte molecules to receptor molecules are detected.