1：Experimental Design and Method Selection:

The study involves the voltage-controlled assembly of 40 nm Au-nanoparticle arrays at a TiN/Ag electrode in contact with an aqueous electrolyte. The methodology includes the use of an optical-electrochemical cell to monitor the assembly and disassembly of nanoparticle arrays under varying electrode potentials.

2：Sample Selection and Data Sources:

The samples used include 4-Mercaptobenzoic acid (4-MBA) functionalized 40±3 nm NPs, 20 mM phosphate buffer (PB, pH

3：2), and 20 mM LiCl. Data sources include reflectance spectra and SERS spectra collected using a custom-built inverted Raman microscope. List of Experimental Equipment and Materials:

Equipment includes a Gamry ref-600 potentiostat, a purpose-built Raman microscope based on an optical inverted microscope (IX71, Olympus), a spectrograph (Shamrock SR-303i, Andor), and an electron-multiplying charge-coupled device camera (EMCCD, Newton DU970BV, Andor). Materials include TiN/Ag substrates, 4-MBA capped 40 nm gold nanoparticles, and various chemicals for NP functionalization.

4：Experimental Procedures and Operational Workflow:

The procedure involves applying varying potentials to the TiN/Ag substrate to control the assembly of NPs, followed by the collection of reflectance and SERS spectra to monitor the changes in optical properties and Raman signal enhancement.

5：Data Analysis Methods:

The analysis includes fitting the experimental reflectance spectra to theoretical models to extract information about the interparticle spacing and using finite-element-method software for numerical simulation of near-field distribution patterns to estimate SERS enhancement factors.