A method for making a plasmonic mushroom array includes: forming a plurality of metal nano-islands each having nanometer-range dimensions on a surface of a glass substrate; and subjecting to the glass substrate having the plurality of metal nano-islands formed thereon to reactive ion etching such that the plurality of metal nano-islands are converted to a plurality of mushroom-shaped structures each having a metal cap supported by a pillar made of a material of the glass substrate and each having dimensions smaller than the dimensions of the nano-islands, the plurality of mushroom-shaped structures being arranged in a substantially regular pattern with intervals smaller than average intervals between the nano-islands, thereby forming the plurality of nano-scale mushroom-shaped structures on the glass substrate that can exhibit localized surface plasmon resonance.