Device design
How the device works: (A) An optical antenna in the form of a single laser-irradiated gold nanoparticle localizes incident laser radiation onto the sample. By raster-scanning the sample underneath the optical antenna the fluorescence signal is recorded pixel by pixel with an avalanche photodiode. A constant separation between the antenna and the sample is maintained based on the detection of the occurring normal forces with a piezoelectric tuning-fork crystal, similar to conventional tapping-mode atomic force microscopy. (B) Electron micrograph showing an 80 nm gold particle attached to the tip of a pointed optical fiber. (Image credit: University of Rochester)