Study of Saturable Scattering of Single Gold Nanoparticle for Super-Resolution Imaging

In the last decade, several super-resolution imaging techniques have been demonstrated to break optical diffraction limit. There are two major underlying mechanisms for all superresolution microscopy: one is to switch on/off the signal, and the other is to saturate the signal. Currently, all techniques rely on switching or saturating fluorescence signals, which exhibit strong limitation on photobleaching and switch repeatability. In this work, we demonstrated novel superresolution imaging based on scattering saturation of a plasmonic particle. We have observed, for the first time, the saturation of scattering in a single gold nanoparticle (GNP), as shown in figure 1. The GNP was excited with three different wavelengths at 405 nm, 532 nm, and 671 nm, and the scattering intensities were measured with a laser scanning confocal microscopy. As a result, the threshold of scattering saturation is lowest at 532 nm, suggesting that saturation is dominated by localized surface plasmon resonance. With the aid of a setup similar to saturable excitation microscopy (SAX) [1], the resolution of scattering image of a single GNP is significantly enhanced. Our study will open up a completely new paradigm for superresolution microscopy.