Figure 22.6 — Optical traps based on plasmonic nanoantennas Figure 22.6 — Optical traps based on plasmonic nanoantennas. (a) Set-up for evanescent wave excitation of a plasmonic nanoantenna (shown in inset; the scale bar is 200 nm). (b) Rayleigh scattering spectra recorded sequentially, showing the shift in the resonance peak indicating the presence of a gold nanoparticle in the gap of a nanoantenna. The discrete steps in the value of the peak wavelength highlighted on the right correspond to one more nanoparticle entering or leaving the gap.Figure (a) is adapted with permission from Righini et al., Nano Lett. 9, 3387–91. Copyright (2009) American Chemical Society.Figure (b) is adapted with permission from Zhang et al., Nano Lett. 10, 1006–11. Copyright (2010) American Chemical Society.