A system for assisting in spectrally characterizing or detecting a sample using radiation at a predetermined wavelength or in a predetermined wavelength range is disclosed. In one aspect, the system includes a substrate having a nanopore for excitation of plasmons. The nanopore provides a window through the substrate, wherein a smallest window opening of the window has an average length (L) and an average width (W) both being substantially smaller than 2 μm. The nanopore supports highly confined surface plasmon polaritons and at specific wavelengths resonances are observed, when the conditions for a standing wave are fulfilled. This leads to strong field enhancements and enables single molecule spectroscopy.