## 3 Results and Discussion  
### Characterization of the rGO-AuNP/ITO Electrode  
GO is highly stable in water and can also be dispersed in an organic solvent due to the presence of oxygen functionalities. It is described as an insulator because of the disruption of its sp\({}^{2}\) bonding networks and a hydroxyl group on or in its surface. However, when it is reduced (rGO), it exhibits a conductivity that can be used in sensor applications [27; 28; 29]. The current responses acquired during the electrochemical deposition of rGO and AuNP on the ITO electrode are shown in Figure 2a. The electrochemical reduction of GO can be expressed as follows [30]:  
\[GO+aH^{+}+be^{-}\to rGO+cH_{2}O \tag{1}\]  
The electrochemical deposition of AuNP determined by the reduction of Au\({}^{3+}\) with HAuCl\({}_{4}\)[31; 32] can be expressed as follows:  
\[HAuCl_{4}+3H^{+}+3e^{-}\to Au+4 HCl \tag{2}\]  
The reductive current showed a significant increase during the first 10 s and 4 s for rGO and AuNP deposition respectively, and gradually reached a stationary value.  
Figure 2b shows the UV-Vis spectra of the rGO-, AuNP-, and rGO-AuNP-deposited ITO substrates using chronoamperometry. From the spectra of the rGO, a shoulder absorption at around 230 nm was caused by an n-\(\pi^{*}\) transition shift of double bonded carbon-oxygen conjugation (C=O; electrons transition from a non-bonding (lone-pair) n orbital to an anti-bonding \(\pi\) orbital called \(\pi^{*}\)). In the case of the AuNP, the absorption peak at about 550 nm was observed due to the resonance frequency in generating the surface plasmon. Therefore, the hybrid layer formation of rGO-AuNP was confirmed by the two UV-Vis absorption peaks at 224\(\rightarrow\)233 nm for rGO and 548\(\rightarrow\)557 nm for AuNP.  
The morphological features of rGO, AuNP and the rGO-AuNP nanocomposite were determined by transmission electron microscope (TEM) and scanning electron microscope (SEM) analysis. Figure 3  
Figure 2: (**a**) Chronoamperograms measured during the electrochemical deposition of reduced graphene oxide (rGO) and gold nanoparticles (AuNP) on the ITO electrode at potentials of \(-\)1.4 V and \(-\)0.9 V vs. Ag/AgCl, respectively, (**b**) UV-Vis absorbance spectra of the rGO-, AuNP-, and rGO–AuNP-deposited ITO substrate using chronoamperometry.  
shows characteristic TEM and SEM images of rGO, AuNP and the rGO-AuNP nanocomposite. rGO has a typical sheet-like structure. In contrast to rGO, the AuNPs exhibited spherical morphologies, evenly distributed with an average size of 15 nm. In addition, the rGO-AuNP hybrid nanocomposite has AuNPs anchored to the surfaces of the rGO. The adhered particles also have spherical morphologies deposited with a diameter of 15 nm on the rGO surfaces. In the rGO-AuNP nanocomposite, the rGO looks like evenly-distributed silky waves of thin sheets, which may be significant in preventing the aggregation of rGO and upholding a surface, enabling the attachment of AuNP to the graphene sheets. The size and density of the AuNPs could be adjusted by controlling the chronoamperometric time, during which the AuNPs were formed by the nucleation and growth of Au deposition. Thus, it was found that the AuNPs were successfully deposited on the rGO/ITO to obtain the hybrid rGO-AuNP/ITO structure via chronoamperometry.  
Figure 3: TEM (**a–c**) and SEM (**d–f**) image of the (**a,d**) rGO-, (**b,e**) AuNP-, and (**c,f**) rGO-AuNO-deposited ITO substrate using chronoamperometry.