Figure 1.

Plasmonic nanopores for single-molecule optical sensing. (a) Schematic side-view illustration of a DNA molecule that is electrophoretically driven through a plasmonic nanopore and detected by optical backscattering from the plasmonic antenna. (b) Illustration of the sensing principle. The temporary presence of the DNA in the hotspot region of the plasmonic antenna induces a shift of the resonance wavelength of the antenna, hence decreasing the scattering intensity that is detected at the excitation laser wavelength. (c) Typical TEM image of the plasmonic nanopore devices used in our experiments. The plasmonic nanopore consists of a gold dimer antenna with a ∼5 nm nanopore at the gap center. The inset shows a false colored TEM image of a zoom of the nanogap region, highlighting the nanopore. (d) Simulated electromagnetic field distribution of the plasmonic nanopore in longitudinal excitation (i.e., with a polarization of the E along the long axis of the structure, cf. image) with a wavelength of 785 nm, as used in our experiments. The simulation shows the extremely enhanced and confined electromagnetic field within the gap of the dimer antenna, which is required for label-free optical sensing of single molecules.