An example of a functionalized plasmonic nanostructure includes a plasmonic nanostructure core; a polymeric hydrogel attached to the plasmonic nanostructure core, the polymeric hydrogel having a thickness ranging from about 10 nm to about 200 nm; and a plurality of primers attached to side chains or arms of the polymeric hydrogel, wherein at least some of the plurality of primers are attached to the polymeric hydrogel at different distances from the plasmonic nanostructure core.