Nonlinear structured-illumination microscopy: Wide-field fluorescence imaging with theoretically unlimited resolution

TLDR: Experimental results show that a 2D point resolution of <50 nm is possible on sufficiently bright and photostable samples, and a recently proposed method in which the nonlinearity arises from saturation of the excited state is experimentally demonstrated.

Abstract: Contrary to the well known diffraction limit, the fluorescence microscope is in principle capable of unlimited resolution. The necessary elements are spatially structured illumination light and a nonlinear dependence of the fluorescence emission rate on the illumination intensity. As an example of this concept, this article experimentally demonstrates saturated structured-illumination microscopy, a recently proposed method in which the nonlinearity arisesfromsaturationoftheexcitedstate.Thismethodcanbeused in a simple, wide-field (nonscanning) microscope, uses only a single, inexpensive laser, and requires no unusual photophysical properties of the fluorophore. The practical resolving power is determined by the signal-to-noise ratio, which in turn is limited by photobleaching. Experimental results show that a 2D point resolution of <50 nm is possible on sufficiently bright and photostable samples.