**3. Materials used in wearable sensors**

Due to the boost in the area of flexible and stretchable electronic materials, various wearable sensor devices have been demonstrated [47]. In order to integrate the wearable sensor with the human body, the mechanical properties of the sensor must be delicate and elastic, and it must be placed on the surface of human skin. Ordinarily, Silicon is the basic material of semiconductor hardware, but its modulus is about 10,000 times higher than that of human skin. Given the huge mechanical inconsistency, the most intuitive approach is to develop electronic materials (**Figure 6**) that are inherently soft to achieve mechanical compatibility and thus implement unrecognizable biosensors. Several review articles on material synthesis, structural engineering, and platform design were published [47–52].
