## 3 Results and Discussions
### Photoamperometric Response with Glucose
However, the linear range observed in this experiment is relatively short, which is approximately 150 nM for both \(CuO\) NPs and NRs. This observation can be attributed to the relatively low quantum efficiency, which generates electron-hole pairs and their recombination. Another significant factor is the limited amount of practical \(CuO\) nanomaterials that act as catalysts for glucose oxidation on the electrode surface. The decrease in photocurrent is attributed to the interaction between the \(CuO\) nanomaterials' surface and glucose in the buffer solution. The reaction mechanisms of non-enzymatic glucose detection using \(CuO\) nanostructures are shown in Figure 11. Due to the semiconductive characteristics of \(CuO\), when the matched light source stimulates, the electrons were stimulated from the valence band (VB) to the conduction band (CB). The transmission of the photoelectron current speed into the solution and the interaction on the surface electrode are faster than the pairing up of the holds on the electrode, which creates the cathode photocurrent. An increase in \(CuO\) promoted the oxidation of glucose to enhance gluconolactone formation. Finally, gluconic acid is formed from glucose. The opposition of photocurrent and glucose concentration is the competition between the cathode photocurrent and the reaction of glucose and \(CuO\); the result of enhanced gluconolactone is the moderation of the transfer and the decrease in the cathode photocurrent. \begin{table}
\begin{tabular}{c c c c c} \hline
**Materials** & **Limit of Detection** & **Linearity Range** & **Density of Photocurrent** & **References** \\ \hline \(CuO\) NPs & 0.69 nM & 3–150 nM & 1–6 \(\mu\)A \(\cdot\) cm\({}^{-2}\) & This work \\ \hline \(CuO\) NRs & 0.61 nM & 3–150 nM & 2–24 \(\mu\)A \(\cdot\) cm\({}^{-2}\) & This work \\ \hline \(Pbs/SiO_{2}/Au\) NPs & 0.46 \(\mu\)M & 1–1000 \(\mu\)M & \(-1.4\)—0.7 \(\mu\)A \(\cdot\) cm\({}^{-2}\) & [25] \\ \hline Cubic structured \(CuO\) & 0.068 \(\mu\)M & 0.001–1.8 mM & 0–2300 \(\mu\)A \(\cdot\) cm\({}^{-2}\) & [46] \\ \hline \(GODx/NDC\)-\(TiO_{2}\) NPs/\(ITO\) & 13 nM & 0.005–10 \(\mu\)M & 0.5–3 \(\mu\)A \(\cdot\) cm\({}^{-2}\) & [51] \\ \hline \(BiVO_{4}\)-MWNT & 22.2 pM & 0.1 nM–1 mM & 1.3–3.5 \(\mu\)A \(\cdot\) cm\({}^{-2}\) & [52] \\ \hline \(BiBr/TiO_{2}\) nanotube arrays & 10 nM & \(5\times 10^{2}\)–\(3\times 10^{7}\)\(\mu\)M & 270–1500 \(\mu\)A \(\cdot\) cm\({}^{-2}\) & [53] \\ \hline \(Au\) modified \(CuO\) NWs & 0.5 \(\mu\)M & 0.5 \(\mu\)M–5.9 mM & 0–7 mA \(\cdot\) cm\({}^{-2}\) & [54] \\ \hline \(LI-NiEC-Cds-G\) & 0.5 \(\mu\)M & 1 \(\mu\)M–1 mM & 20–90 \(\mu\)A \(\cdot\) cm\({}^{-2}\) & [55] \\ \hline \(3\)D hollow-out & 8.7 \(\mu\)M & 0–2 mM & 264.5–382.3 \(\mu\)A \(\cdot\) cm\({}^{-2}\) & [56] \\ \hline \(CDs/B-TiO_{2}/GO_{x}\) & 43 \(\mu\)M & 0–9 mM & 19.8–34.63 \(\mu\)A \(\cdot\) cm\({}^{-2}\) & [57] \\ \hline \(TiO_{2}/SrTiO_{3}/PDA/GO_{x}\) & 25.68 \(\mu\)M & 0–32 mM & 601.9–773.74 \(\mu\)A \(\cdot\) cm\({}^{-2}\) & [58] \\ \hline \(TiO_{2}/rGO/PDA/GO_{x}\) & 0.034 \(\mu\)M & 0–3 mM & 85.7–127.16 \(\mu\)A \(\cdot\) cm\({}^{-2}\) & [59] \\ \hline \end{tabular}
\end{table} 
Table 1: Comparison of linear range, density of photocurrent, and limit of detection of various PEC sensors for glucose testing. The photocurrent density of \(ITO/CuO\) NRs ranged from 2 to 24 \(\mu\)A \(\cdot\) cm\({}^{-2}\), which was three times higher than that of \(ITO/CuO\) NPs (Figure 9). This superior performance of \(CuO\) NRs is based on several key factors. Firstly, they exhibit strong light absorption across a broad wavelength range (350-800 nm), as shown by the absorbance curve in Figure 5. This enhanced absorption, particularly under concentrated light conditions, leads to better compatibility with the utilized light source. \(CuO\) NRs with a bandgap of 1.59 eV effectively prevent the recombination of electron-hole pairs. On the other hand, \(CuO\) NPs and \(CuO\) NSs have lower bandgaps of 1.33 eV and 1.32 eV in Tauc plots.