Resolution enhancement of saturated fluorescence emission difference microscopy.

Fluorescence emission difference microscopy (FED) obtains resolution-enhanced images by subtracting acquired solid and doughnut confocal images. Because of the mismatch of the outer contours of the two subtraction components, negative values are inevitable in the conventional FED method, giving rise to deformations. In this study, by using a saturation effect, we obtain imaging results with a profile-extended solid and center-shrunken doughnut point spread function. Owing to the nonlinear effect, two better-matched saturated images not only eliminate the deformations, but also enhance the resolving ability and signal to noise ratio compared to conventional FED. Simulations based on the saturated model of rhodamine 6G, as well as experiments on biological samples, are presented to verify the capability of the proposed concept, while experimental results show the unprecedented resolving ability of the saturated FED method.