Superresolution imaging based on nonlinearity of plasmonic scattering
Shi-Wei Chu1*
1Physics, National Taiwan University, Taipei, Taiwan
* presenting author:朱士維,
This year, the Nobel Chemistry Award was given to three physicists working on the development of superresolution microscopy. During the last decade, the diffraction limit of resolution was beautifully overcome by manipulating the on/off switching of fluorophores, or by saturation of fluorescence emission, resulting in resolution below 100 nm. Nevertheless, fluorescence exhibits intrinsic photobleaching issue. Therefore, it will be more than desirable to develop superresolution imaging modality based on an alternative contrast agent without bleaching, such as scattering. It is known that plasmonic nanoparticles exhibit extraordinarily strong scattering due to surface plasmon resonance (SPR). To our knowledge, neither saturation, nor switching of scattering from SPR structures has been reported, but there are plenty of reports on saturable absorption of plasmonic nanoparticles embedded in dielectric matrix. Since scattering and absorption are related to the real and imaginary parts of electric susceptibility, respectively, we expect to find saturable scattering with plasmonic particles.
Here we feature the first demonstration of scattering saturation in a single 80-nm gold nanoparticle. It is clear that saturation of scattering is observed for those wavelengths located within the SPR band, and no saturation is observed for the wavelength outside the SPR band. This result suggested that the scattering saturation is governed by localized SPR in the nanoparticle. By extracting the saturated part inside the focal region, and with the aid of extra field localization due to SPR saturation, we have achieved sub-80-nm spatial resolution. Potential applications range from biomedical imaging to functional inspection of plasmonic nanostructures.

Keywords: optical microscopy, resolution, gold nanoparticle, surface plasmon resonance, saturation