A method of increasing a surface-enhanced Raman scattering (SERS) signal of a compound is provided. The method includes dissolving the compound in water to form a solution, adding a substrate at least partially coated with gold nanoparticles to the solution to form a mixture, removing the substrate from the mixture and washing with water to form a SERS sample having at least a portion of molecules of the compound adsorbed to the gold nanoparticles on the substrate, and recording a SERS spectrum of the SERS sample. The gold nanoparticles are in a two-dimensional (2D) monolayer assembly on the substrate and are 10-250 nm in size. The SERS signal of the SERS spectrum is higher than a SERS signal of a SERS spectrum of the compound on the substrate without the gold nanoparticles.