An apparatus for performing surface enhanced Raman spectroscopy (SERS) includes a substrate and a plurality of nano-pillars, each of the plurality of nano-pillars having a first end attached to the substrate, a second end located distally from the substrate, and a body portion extending between the first end and the second end, in which the plurality of nano-pillars are arranged in an array on the substrate, and in which each of the plurality of nano-pillars is formed of a polymer material that is functionalized to expand in the presence of a fluid to cause gaps between the plurality of nano-pillars to shrink when the fluid is supplied onto the nano-pillars.