A first plasmonic-nanostructure sensor pixel includes a semiconductor substrate and a plurality of metal pillars. The semiconductor substrate has a top surface and a photodiode region therebeneath. The plurality of metal pillars is at least partially embedded in the substrate and extends from the top surface in a direction substantially perpendicular to the top surface. A second plasmonic-nanostructure sensor pixel includes (a) a semiconductor substrate having a top surface, (b) an oxide layer on the top surface, (c) a thin-film coating between the top surface and the oxide layer, and (d) a plurality of metal nanoparticles (i) at least partially between the top surface and the oxide layer and (ii) at least partially embedded in at least one of the thin-film coating and the oxide layer. A third plasmonic-nanostructure sensor pixel includes features of both the first and second plasmonic-nanostructure sensor pixels.