Herein, we report polydimethylsiloxane (PDMS) based optical sensing platforms and describe how they can be tuned, using nanomaterials, to exhibit plasmonic properties that can be exploited for sensing applications. The platforms include a colorimetric-based sensor realized on gold nanoparticles grown on PDMS films. A theoretical model based on finite element analysis was developed in order to describe the optical behavior and the functional properties of these plasmonic transducers. We demonstrate the ability of these systems to detect even small changes in the refractive index of the external environment, predicting the evolution of their sensing performance. We have experimentally explored the modulation of the plasmonic properties of these platforms by monitoring the shift of the typical localized surface plasmon resonance peak in order to explore potential plasmon-enhanced functionality.