**5. Type of Transducers**

A transducer is considered a significant part of the biosensor. It can convert the physical change of the surroundings to suitable electrical signals, which a reaction could cause. Biological or bio-recognition elements can be associated with or integrated with a transducer. The bio-recognition elements can be incorporated with chemical and physical bounding on the surface of the transducer, which also depends on the immobilization methods [97]. Significant electrochemical transducers are available, such as amperometric or voltammetric, impedimetric, capacitive, potentiometric, and ion-selective field-effect transistors. The following sections summarise these transducers for water quality detections in various applications. As is shown in Table 3, various types of transducers and characteristics were summarized.
