fig2

Figure 2. Response mechanisms of enzymatic electrochemical sensors and enzyme immobilization methods. (A) Schematic illustration of the first-generation enzymatic sensor utilizes the concept of electrocatalytic detection; (B) Schematic representation of the second-generation enzymatic sensor incorporates redox mediators; (C) The third-generation enzymatic sensor; (D) Schematic illustration for physical enzyme immobilization of soaking method, drying method, entrapment method, and ionic binding, respectively; (E) Diagram illustrating enzyme immobilization of chemical methods of covalent bonding and crosslinking, respectively.