Multicolor re-scan super-resolution imaging of live cells.

Background: Multicolor fluorescence microscopy has proved essential in biological studies. However, the application of conventional multicolor microscopy to imaging subcellular organelles is restricted by its diffraction-limited spatial resolution. Re-scan confocal microscopy (RCM), a novel super-resolution imaging technique, can effectively address this problem. However, previous multicolor RCM imaging methods usually led to spatial mismatch in images due to the sequential scanning of the sample with multiple excitation lasers.

Methods: We present a new RCM system to achieve multicolor super-resolution imaging. A spectrograph was used as the multicolor detection system, and a linear spectral unmixing algorithm was applied to separate different fluorophores in the spectral image. Moreover, since the image reconstruction process induced an artificial resolution improvement, a gamma correction was introduced to restore the multicolor super-resolution image.

Results: By imaging phalloidin-labeled F-actin in breast cancer cells, we found that the lateral resolution of our system is approximately 171 nm, which is a 1.8-fold improvement over that of wide-field imaging. The successful identification of three types of fluorescent beads indicated that our multicolor RCM can resolve different fluorophores whose spectra largely overlap with each other. Finally, we demonstrated that our method is suitable for imaging multicolor-labeled organelles of live cells.

Conclusions: Our novel RCM system can acquire multicolor super-resolution images of live cells without spatial mismatch, obvious photobleaching or photodamage. This system may provide a new imaging tool for monitoring dynamic events involving interactions between multiple molecules and organelles in cells.