Superresolution microscopies have revolutionized optical imaging field in the last decade by providing a novel capability for nanoscale observation with visible light. Current techniques mostly rely on switching or saturation of fluorescence, but suffer from limited imaging depth due to the requirement of special illumination patterns (STED, SIM), or the lack of optical sectioning capability (localization microscopy). Saturated excitation (SAX) microscopy provides the potential for deep-tissue resolution enhancement due to its laser-scanning nature without additional beam shape engineering. However, for current fluorescence SAX microscopy, it is difficult to achieve resolution better than 100-nm, limited by the difficulty to obtain high order demodulation as well as by photobleaching due to high-intensity illumination.
Our recent finding revealed that the bleaching issue in SAX could be resolved by substituting fluorescence with scattering from metallic nanoparticles. From the scattering-based experiment, we realized that the resolution limit of SAX could be significantly improved by proper nonlinear response of emitters. In this paper, we show that with suitable nonlinear power dependence, either scattering or fluorescence, SAX microscopy can provide sub-20-nm spatial resolution at relatively low power. Our work provides not only a new concept to enhance resolution with saturation-based techniques, but also a novel example toward ultrahigh resolution imaging with a laser-scanning scheme.
Hou-Xian Ding, Kuan-Yu Li, Gitanjal Deka, I-Cheng Su, and Shi-Wei Chu, "Resolution enhancement down to 10-nm based on saturated excitation (SAX) microscopy plus novel nonlinear response (Conference Presentation)," Proc. SPIE 10071, Single Molecule Spectroscopy and Superresolution Imaging X, 100710G (Presented at SPIE BiOS: January 29, 2017; Published: 24 April 2017); https://doi.org/10.1117/12.2251301.5380386349001.
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