High-speed TIRF and 2D super-resolution structured illumination microscopy with a large field of view based on fiber optic components

Improved tools for live imaging of F-actin structures in yeast

For over 20 years, the most effective probe for live imaging of yeast actin cables has been Abp140-GFP. Here, we report that endogenously-tagged Abp140-GFP poorly decorates actin patches and cables in the bud compartment of yeast cells, while robustly decorating these structures in the mother cell. Using mutagenesis, we found that asymmetric decoration by Abp140 requires F-actin binding. By expressing integrated Bni1-Bnr1 and Bnr1-Bni1 chimeras, we demonstrate that asymmetric cable decoration by Abp140 also does not depend on which formin assembles the cables in each compartment. In contrast, the short actin-binding fragment of Abp140 (known as "Lifeact"), fused to 1x or 3xmNeonGreen and expressed from the endogenous ABP140 promoter, uniformly decorates patches and cables in both compartments. Further, this probe dramatically improves live imaging detection of cables (and patches) without altering their in vivo dynamics or cell growth. Improved detection allows us to visualize cables growing inward from the cell cortex and dynamically interacting with the vacuole. This probe also robustly decorates the cytokinetic actomyosin ring. Because Lifeact-3xmNeon expressed at relatively low levels provides intense labeling of cellular F-actin structures, this tool may improve live imaging in other organisms where higher levels of Lifeact expression are detrimental.

Correlative single-molecule and structured illumination microscopy of fast dynamics at the plasma membrane

Total internal reflection fluorescence (TIRF) microscopy offers powerful means to uncover the functional organization of proteins in the plasma membrane with very high spatial and temporal resolution. Traditional TIRF illumination, however, shows a Gaussian intensity profile, which is typically deteriorated by overlaying interference fringes hampering precise quantification of intensities-an important requisite for quantitative analyses in single-molecule localization microscopy (SMLM). Here, we combine flat-field illumination by using a standard πShaper with multi-angular TIR illumination by incorporating a spatial light modulator compatible with fast super-resolution structured illumination microscopy (SIM). This distinct combination enables quantitative multi-color SMLM with a highly homogenous illumination. By using a dual camera setup with optimized image splitting optics, we achieve a versatile combination of SMLM and SIM with up to three channels. We deploy this setup for establishing robust detection of receptor stoichiometries based on single-molecule intensity analysis and single-molecule Förster resonance energy transfer (smFRET). Homogeneous illumination furthermore enables long-term tracking and localization microscopy (TALM) of cell surface receptors identifying spatial heterogeneity of mobility and accessibility in the plasma membrane. By combination of TALM and SIM, spatially and molecularly heterogenous diffusion properties can be correlated with nanoscale cytoskeletal organization and dynamics.

Full field-of-view hexagonal lattice structured illumination microscopy based on the phase shift of electro-optic modulators

High throughput has become an important research direction in the field of super-resolution (SR) microscopy, especially in improving the capability of dynamic observations. In this study, we present a hexagonal lattice structured illumination microscopy (hexSIM) system characterized by a large field of view (FOV), rapid imaging speed, and high power efficiency. Our approach employs spatial light interference to generate a two-dimensional hexagonal SIM pattern, and utilizes electro-optical modulators for high-speed phase shifting. This design enables the achievement of a 210-µm diameter SIM illumination FOV when using a 100×/1.49 objective lens, capturing 2048 × 2048 pixel images at an impressive 98 frames per second (fps) single frame rate. Notably, this method attains a near 100% full field-of-view and power efficiency, with the speed limited only by the camera's capabilities. Our hexSIM demonstrates a substantial 1.73-fold improvement in spatial resolution and necessitates only seven phase-shift images, thus enhancing the imaging speed compared to conventional 2D-SIM.

Grazing incidence to total internal reflection fluorescence structured illumination microscopy enabled by a prism telescope

In super-resolution structured illumination microscopy (SR-SIM) the separation between opposing laser spots in the back focal plane of the objective lens affects the pattern periodicity, and, thus, the resulting spatial resolution. Here, we introduce a novel hexagonal prism telescope which allows us to seamlessly change the separation between parallel laser beams for 3 pairs of beams, simultaneously. Each end of the prism telescope is composed of 6 Littrow prisms, which are custom-ground so they can be grouped together in the form of a tight hexagon. By changing the distance between the hexagons, the beam separation can be adjusted. This allows us to easily control the position of opposing laser spots in the back focal plane and seamlessly adjust the spatial frequency of the resulting interference pattern. This also enables the seamless transition from 2D-SIM to total internal reflection fluorescence (TIRF) excitation using objective lenses with a high numerical aperture. In linear SR-SIM the highest spatial resolution can be achieved for extreme TIRF angles. The prism telescope allows us to investigate how the spatial resolution and contrast depend on the angle of incidence near, at, and beyond the critical angle. We demonstrate this by imaging the cytoskeleton and plasma membrane of liver sinusoidal endothelial cells, which have a characteristic morphology consisting of thousands of small, transcellular pores that can only be observed by super-resolution microscopy.