Three-Dimensional Plasmonic Nanorod Location and Orientation Sensing Based on Double Fano Resonances

The sensing of spatial positions and orientations at the nanometre scale is of significance for studying complex macromolecular and biological processes, as well as their dynamic evolution. Herein, plasmonic nanorod location and orientation sensing both inside and outside a three-dimensional (3D) plasmonic nanosystem are achieved based on double Fano resonances. The numerical simulation and analysis show that these two Fano resonances are found to originate from different physical mechanism. One is attributed to the excitation of the quadrupole mode supported by the upper nanorod pair, and the other arises from the excitation of the quadrupole mode in the lower nanorod pair. Owing to the different origins, these two Fano resonances exhibit quite different responses to the configuration changes inside and outside the plasmonic nanosystem. Specifically, the configuration changes inside the nanosystem are identified by retracing the first Fano resonance. When the foreign nanorod intrudes into the plasmonic nanosystem, the second Fano resonance emerges. By reading out the second Fano resonance spectral response, which takes the first Fano resonance as the reference, the spatial positions and orientations of the foreign nanorod are determined. This work opens up new opportunities for developing advanced nanooptical devices, which can be applied to 3D macromolecule configuration information retrieval and dynamic biological process analysis by providing a complete picture of time-dependent nanoscale motions and rearrangements.