## 3 Results and Discussions
### Photoamperometric Response with Glucose  
Figure 9a depicts the photocurrent response of the \(ITO/CuO\) (NPs, NRs, and NPs) electrodes in 100 nM glucose dissolved in PBS solution under 395 nm LED light irradiation at an applied potential of 0.2 V. Under illumination, the \(ITO/CuO\) NRs electrode exhibits the highest photocurrent (5.5 uA), while other electrode types show lower values (around 2 uA). Figure 9b-d reveal the photocurrent response of the \(ITO/CuO\) electrodes to different glucose concentrations (0-150 nM). In particular, \(ITO/CuO\) NRs and \(ITO/CuO\) NPs exhibit a linear decrease in photocurrent with increasing glucose concentration, indicating a sensitive response. However, the \(ITO/CuO\) NSs electrode does not show this linear behavior. Following the response of photocurrent to the glucose concentrations, it is obvious that the photocurrent density decreased steadily, which is proportional to the increasing glucose concentration. However, the photocurrent signal of the \(ITO/CuO\) NSs was neither stable nor linearly increasing, as shown in Figure 9d. Therefore, the results focused on the linearity of \(ITO/CuO\) NPs and \(ITO/CuO\) NRs. Figure 10 illustrates the response of the photocurrent to the glucose concentration of \(ITO/CuO\) NPs (Figure 10a) and \(ITO/CuO\) NRs (Figure 10b), which include two linear regions. For the \(ITO/CuO\) NPs, the results has the following these lines: J (uA\(\cdot\)cm\({}^{-2}\)) = \(-0.180\cdot\) C (nM) + 7.0553 and J (uA \(\cdot\) cm\({}^{-2}\)) = \(0.018\cdot\) C (nM) + 3.805, while the linear line fitting of \(ITO/CuO\) NRs are J (uA \(\cdot\) cm\({}^{-2}\)) = \(-0.6581\cdot\) C (nM) + 21.606 and J (uA \(\cdot\) cm\({}^{-2}\)) = \(-0.04488\cdot\) C (nM) + 8.7798; in which J is the density of photocurrent, C is the glucose concentration, and the correlation coefficient (R2) is higher than 0.9. The relative standard deviations (RSDs) of eight \(ITO/CuO\) NPs samples were 0.38% and 0.84%, respectively. The limit of detection (LOD) was calculated by the formula LOD = 3 \(\sigma\)/s (\(\sigma\) is the standard deviation of the blank signal and s is sensitivity) [50]. The calculated LODs of \(ITO/CuO\) NPs and \(ITO/CuO\) NRs are 0.69 nM and 0.61 nM  
Figure 8: Electrochemical impedance spectroscopy of (**a**) \(CuO\) NPs, (**b**) \(CuO\) NRs, and (**c**) \(CuO\) NSs sprayed on \(ITO\) electrodes with and without light irradiation. glucose, respectively. Additionally, the photoelectrochemical performance of the \(CuO\) nanostructures' electrodes was compared with the other photoelectrochemical glucose sensing reports, as summarized in Table 1. Our \(ITO/CuO\) nanostructures, including the NPs and NRs, exhibited competitive performance, high sensitivity (3-150 nM), and a low detection limit. Figure 10: Corresponding calibration curve of (**a**) \(ITO/CuO\) NPs electrode and (**b**) \(ITO/CuO\) NRs electrode. Figure 9: (**a**) Comparison of photocurrent responses of three types of \(ITO/CuO\) nanostructures to 100 nM glucose at an applied potential of 0.2 V (vs. \(Ag/AgCl\)) under 395 nm LED irradiation. Photocurrent responses of (**b**) \(ITO/CuO\) NPs, (**c**) \(ITO/CuO\) NRs, and (**d**) \(ITO/CuO\) NSs electrodes at different glucose concentrations from 0 to 150 nM. The \(CuO\) nanostructures exhibit the sensitivity to glucose at the nanomolar level, which is attributed to the nanosized structure of the material deposited onto the \(ITO\) electrode, and the essential role of the PEC method in detecting extremely low-level signals is due to its ability to eliminate background noise. These \(CuO\) NPs and \(CuO\) NRs exhibited two linear ranges. This linearity arises from the generation of electrons for the oxidation of glucose, which continues until signal saturation. The subsequent linear range may have resulted from the enhanced adsorption of glucose molecules on the effective surface of the \(CuO\) nanomaterials as the glucose concentration increased.