Tuning the properties of optical metamaterials in real time is one of the grand challenges of photonics. Being able to do so will enable a new class of photonic materials for use in applications such as surface enhanced Raman spectroscopy and reflectors/absorbers. One strategy to achieving this goal is based on the electrovariable self-assembly and disassembly of two-dimensional nanoparticle arrays at a metal liquid interface. As expected the structure results in plasmonic coupling between NPs in the array but perhaps as importantly between the array and the metal surface. In such a system the density of the nanoparticle array can be controlled by the variation of electrode potential. Due to the additive effect, we show that less than 1 V variation of electrode potential can give rise to a dramatic simultaneous change in optical reflectivity from ~93 % to ~1 % and the amplification of the SERS signal by up to 5 orders of magnitude. The process allows for reversible tunability. These concepts are demonstrated in this manuscript, using a platform based on the voltage-controlled assembly of 40 nm Au-nanoparticle arrays at a TiN/Ag electrode in contact with an aqueous electrolyte. We show that all the physics underpinning the behaviour of this platform works precisely as suggested by the proposed theory, setting the electrochemical nanoplasmonics as a promising new direction in photonics research.