## 3 Mechanism of Cyclic Voltammetry Transducer  
With consideration of all the advantages of the electrochemical properties of the graphene-based electrode, electrochemical biosensors have been developed widely. The non-enzymatic glucose sensor is defined as an electrochemical biosensor that uses its electrode as an electrocatalytic to measure glucose concentration [79]. Electrochemical detection principles lie behind the measurement for physicochemical properties of the bioreactor and target analyte to create a readable signal, such as electrical current, voltage, resistance, etc. If the chemical reaction between the target analyte and bioreactors (electrode) happens, the electrical properties of the solution changes due to the production of ion or electron [79; 80]. In general, electrochemical detection techniques could be categorized as amperometric-based, impedimetric-based, potentiometric-based, or conductometric-based. An amperometric-based electrochemical biosensor is most widely used for the non-enzymatic glucose sensor [81; 82; 83; 84; 85; 86; 87; 88; 89; 90; 91; 92; 93; 94; 95; 96; 97; 98; 99; 100; 101; 102; 103; 104; 105; 106; 107; 108; 109; 110; 111; 112; 113; 114; 115; 116; 117; 118; 119; 120; 121; 122; 123; 124; 125; 126; 127; 128; 129; 130; 131; 132; 133; 134; 135; 136; 137; 138; 139; 140; 141; 142; 143; 144; 145; 146; 147; 148; 149; 150; 151; 152; 153; 154; 155; 156; 157]. Cyclic voltammetry (CV) is considered as an amperometric detection method [82]. While the electrocatalytic electrochemical properties of the electrode towards GOx could be characterized using the CV method, the redox potential based on the applied voltage at the working electrode surface could be analyzed [83; 84]. In general, the cell contains three electrodes: Working electrode (WE--where the electrochemical action happens), reference electrode (RE--as a reference point to measure the potential for the other electrodes), and the counter electrode (CE--complete the circuit). A potentiostat is connected between WE and RE to apply a different potential. The integrated three electrodes of the CV cell work as the main components of the CV cell [85]. The applied voltage creates a potential for the chemical reaction at the electrode surface, where the reactance molecule moves to the electrode surface for mass interaction, then the electrode receives the chemical signal using the electron quantum tunneling concept (less than 2 nm of the electron tunneling distance) that leads to generating a current flow through the electrode that could be measured in a cyclic manner. This cyclic process gives information about the oxidation and reduction at the electrode surface using the following chemical equation [86; 87]:  
\[\mathrm{O}+\mathrm{n}e^{-}\rightleftharpoons\mathrm{R} \tag{8}\]  
Hence, the electrochemical reaction rate and redox potentials can be performed using single or multiple cycles. The graph of current vs. the applied voltage is called the cyclic voltammogram curve, where all the data of oxidation or reduction information is recorded at the working electrode [88]. Figure 5 shows a CV cell simulation and components with all the details of the electrical circuit scheme. Figure 5: (**A**) A three-electrode cell with the utilization of cyclic voltammetry (CV) detection method—the input is the applied voltage while the output is the electrochemical analysis through the cyclic voltammogramcurve. (**B**) CV cell circuit--when the voltage applied to the electrochemical reaction starts on the electrode surface then the current starts to flow. (**C**) Simulation of electrode reaction with the reactant (glucose)--at a given applied voltage the reactant starts to move towards the electrode surface then the quantum tunneling happens to the electron, as a result, the reaction occurs to form the product. Table 2 shows the main equations of the CV cell with the basic definitions. The oxidation and reduction at the graphene composites electrode surface could be understood using the Fermi-level energy (FE).