Nanoclusters and nanogap formation may be explained by the interplay between mass transport (diffusion and electron migration) of Ag ions and passivation by Gum Arabic. After mixing with Gum Arabic, the resistance of the mixed solution is higher than AgNO3 alone. This was inferred by the recordings of the electrical current when using solutions with and without Gum Arabic, see SI Figure (A) and Figure . Using the same deposition parameter as S4 (-0.2 V, 2 s; -0.8 V, 8 s), the maximum deposition current was about 2 µA without Gum Arabic, while it was around 120 nA after mixing AgNO3 with Gum Arabic. The reduction of Ag ions to Ag atoms reaction happened on the substrate emanating away from the electrodes due to the strong electric field. The Ag-GA complex formed immediately and stacked on the SiO2/Si substrate. The formation of Ag-GA nanoclusters further affected the electric field distribution and helped the formation of nanogaps in between the nanoclusters. As different concentrations of Gum Arabic solutions had different resistances, it was observed that the resistance increased as the concentration of Gum Arabic increased within certain Gum Arabic concentrations. According to Ohm's law, J= σ E, where J is the current density, σ is the electrical conductivity, E is electric field, different concentrations of Gum Arabic solutions resulted in different electrical conductivity for the mixed silver precursor solutions, which further resulted in different current densities in the electrochemical system. Thus, there were different Ag-GA nanostructures formed with different Gum Arabic concentrations when the other deposition parameters were maintained (see structure 1, 3, 4 and SI Figure ).). The applied voltage also affected the growth pattern and growth direction of the Ag-GA nano particles (see structure 1, 2 and SI Figure ). The detailed discussion is presented in SI. In conclusion, by adjusting the concentration of AgNO3 and Gum Arabic in the solution as well as the electrochemical deposition parameters such as applied voltage and deposition time, it is possible to engineer the size and morphology of the Ag-GA nano structures and the nano gap patterns in between the nano clusters. The high density of nanostructures and nano gaps made these substrates good candidates for SERS applications. Step 1: -0.2 V, 2s;