**4. Dyes in electrochemical biosensors**

Electrochemical biosensor is capable of providing specific quantitative or semiquantitative analytical information using electrochemical transduction elements, e.g., charge-transfer complexes. Low-cost, energy efficient, portable, easy fabrication, and real-time sensing are major advantages of electrochemical biosensing platforms. Among the electrical signal molecules, there are several types of dyes with electrochemical activity, and they will be introduced in this part. In addition, the electrochemical signals generation mechanisms are explained and applications of these dyes as labels in the biosensors are also displayed.
