Plasmon ruler based on Fano resonance of a square ring-disk trimer nanostructures

We report a plasmon ruler based on Fano resonance of a trimer nanostructure composed of a concentric square ring-disk and an outside cuboid nanoparticle. The Fano resonance wavelength shifts blue with increasing the gap between the concentric square ring-disk and the outside cuboid, and with the rotation of the outside cuboid. Compared with the fractional shift of the plasmon resonance, the sensitivity is enhanced by 20–80 times, approaching to 1 Å or 1°, if Fano features are considered. These results indicate that plasmon ruler based on Fano resonance improves the sensitivity in a very efficient way.