Superimposed Arrays of Nanoprisms for Multispectral Molecular Plasmonics

Molecular plasmonics relies on the development of conductive nanostructures to yield large local electromagnetic enhancement enabling the detection of molecules located in their vicinity. Although various spectroscopic techniques benefit from such enhancement, performing different spectroscopic measurements on the same platform remains a challenge. As such, the rational design of structures capable of enhancement effects over a large spectral range, particularly from the visible to the mid-infrared, is of great interest. Herein, we have developed a series of metallic patterns, consisting of superimposed arrays of gold nanoprisms, that have the potential for surface-enhanced Raman spectroscopy (SERS), surface-enhanced fluorescence (SEF), and surface-enhanced infrared absorption (SEIRA). We first demonstrate that a modified version of the nanosphere lithography method can be used to fabricate such platforms. Patterns with selected sizes can further be produced by electron-beam lithography with virtually no defects, thus yielding tunable and precise optical resonances from the visible to the mid-infrared range. The hexagonal lattices were composed of smaller prisms (0.25 μm prism base length) incorporated for SERS and SEF applications and larger triangles (1–2 μm base size) for SEIRA purposes. The superimposed patterns display regions that are compatible with SEF, SERS, and SEIRA, thus opening promising applications for multispectral detection of molecules.