1：Experimental Design and Method Selection:

The study used two reducing agents, sodium citrate and sodium borohydride, to synthesize Au-NPs. The dependency of size, polydispersity, surface potential, plasmonic spectrum, and pH on the reducing agents' concentrations was investigated.

2：Sample Selection and Data Sources:

Au-NPs were synthesized in sizes ranging from 2.5 to 35nm. The samples were characterized using UV-Vis absorption spectroscopy, Dynamic Light Scattering (DLS), and Transmission Electron Microscopy (TEM).

3：5 to 35nm. The samples were characterized using UV-Vis absorption spectroscopy, Dynamic Light Scattering (DLS), and Transmission Electron Microscopy (TEM). List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Perkin-Elmer 25 UV-Vis spectrometer, Zetasizer Nano Series from Malvern for DLS, Zeiss-EM10C electron microscope for TEM, and chemicals including tri-sodium citrate, chloroauric acid, sodium borohydride, and ultrapure deionized water.

4：Experimental Procedures and Operational Workflow:

For sub-10nm NPs, sodium borohydride was used as the reducing agent. For NPs larger than 20nm, tri-sodium citrate was used. The synthesis conditions were varied to study the effect of reducing agent concentration on the properties of Au-NPs.

5：Data Analysis Methods:

The size distribution, polydispersity index, and Zeta potential were measured using DLS. The absorption spectra were recorded to study the plasmonic properties of Au-NPs. TEM images were analyzed to confirm the size and morphology of the nanoparticles.