*1.4.1 Electrochemical biosensors*

Electrochemical biosensors are simple devices that use bioelectrodes to measure electric current, ionic, or conductance changes. These biosensors have different types according to the transducer deployed and also based on the measurements of electrical parameters including potentiometric, amperometric, and voltammetric biosensors. The electrochemical biosensor has three electrodes namely reference, working, and counter electrodes [1]. A typical example of the electrochemical biosensor is shown in **Figure 3**.

*Recent Advances in Biosensing in Tissue Engineering and Regenerative Medicine DOI: http://dx.doi.org/10.5772/intechopen.104922*

#### **Figure 3.**

*A schematic representation of an electrochemical biosensor illustrating its application in enzyme, antibody, or aptamer measurements [20].*

#### **Figure 4.**

*A schematic representation of a piezoelectric sensor. (a) Target antigen and antibody on a piezoelectric material before and after binding, (b) voltage-time curve before and after binding in a piezoelectric sensor and (c) amplitude of a piezoelectric sensor before and after binding concerning frequency [21].*

#### *1.4.2 Piezoelectric biosensors*

They produce an electrical signal based on the principle of acoustics (sound vibrations) when mechanical force is applied. Quartz crystals are a common piezoelectric material used in biosensors. **Figure 4** displays a commonly used piezoelectric biosensor.

#### **Figure 5.**

*A schematic representation of an optoelectrical arrangement of an optical biosensor [24].*
