## 3 Results and Discussion
### Characterization of the Developed Substrates
The change in the microscopic surface area of the electrode produced by the oxidation-reduction cycles is proportional to the oxidation peak, as [PERSON] and [PERSON] mentioned in [18; 19]. Therefore, a higher oxidation peak indicates that more nanostructures were produced on the electrode surface during the oxidation-reduction scanning process. Figure 5: The cyclic voltammetry curves from the 1 st scan to the 15 th scan cycle at a sweeping rate of 50 mV s\({}^{-1}\) in the 0.2 M KCl solution. Each cycle curve was plotted in a different line style for clarity. The position of the blue arrow in the figure shows the position where the oxidation peak occurs, which is about 530 mV. We can see from the figure that the oxidation peak current increases with the number of scanning cycles. However, the increment gradually reduces, and its increment was quite limited after the number of scanning cycles exceeded 10. SERS measurements of substrates electrochemically treated with different oxidation-reduction cycles were conducted for comparison. From the SERS spectra of 1 \(\upmu\)M R6G solution measured by substrates with different oxidation-reduction cycle times (0, 2, 4, 6, 8, 10, 12, and 14, respectively), the SERS characteristic peak intensity of R6G at 1510 cm\({}^{-1}\) increase rapidly in the first few cycles and reach a plateau after 10 cycles (as shown in Figure 7). It has the same tendency as the oxidation peak of the redox curve shown in Figure 6. This is because higher oxidation peaks indicate more reaction surface area, which means more nanostructures were created. More nanostructures not only have a larger reaction area but also produce higher density SERS hot spots and lead to higher SERS intensities. Therefore, the optimal number of oxidation-reduction cycles can be determined by monitoring the oxidation-reduction plots. Once it reaches a plateau state, it means the optimal oxidation-reduction cycles for SERS enhancement has been reached. Figure 6: The oxidation peak currents at 530 mV were plotted against the scanning cycles. It can be seen that the oxidation peak current increases with the number of scanning cycles. The increment gradually reduces, and when the voltammetry redox scan reaches a certain amount of cycles (in this case around 10 cycles), the oxidation peaks reach a plateau state. Figure 7: It shows the surface-enhanced Raman scattering (SERS) experiments results of 1 \(\upmu\)M Rhodamine 6 (R6G) solution measured by SERS chips with different oxidation-reduction cycles (0, 2, 4, 6, 8, 10, 12, and 14, respectively). It can be seen that in the first few cycles, the intensity of the SERS characteristic peak of R6G at 1510 cm\({}^{-1}\) increased rapidly and reached a plateau after 10 cycles. Another note worth mentioning is that the peak current of the reduction is less than the peak oxidation current, which means that the redox process is irreversible. Therefore, the gold film on the surface of the pyramid is gradually oxidized and dissolved. This will cause the gold film on the surface of the pyramid to gradually decrease. This is why too many redox scan cycles can cause the gold film to become too thin and expose the underlying pyramid (as shown in Figure 4). Therefore, we need to carefully monitor the oxidation-reduction curves and stop the oxidation-reduction process once the oxidation peak reaches a plateau.