This protocol describes how to assemble a 4Pi single-molecule switching (SMS or SMLM) super-resolution microscope. Detailed instructions for beam-path alignment, testing, application to cellular samples, and troubleshooting are provided.TWEET New Protocol for setting up a 4Pi super-res microscope from @MicronOxford @GurdonInstitute @JonasRies and @bewersdorflab COVER TEASER Implementing a 4Pi super-resolution microscope
ABSTRACTThe development of single-molecule switching (SMS) fluorescence microscopy (also called singlemolecule localisation microscopy (SMLM)), over the last decade has enabled researchers to image cell biological structures at unprecedented resolution. Using two opposing objectives in a so-called 4Pi geometry doubles the available numerical aperture, and coupling this with interferometric detection, has demonstrated three-dimensional (3D) resolution down to 10 nm over entire cellular volumes. The aim of this protocol is to enable interested researchers to establish 4Pi-SMS super-resolution microscopy in their laboratories. We describe in detail how to assemble the optomechanical components of a 4Pi-SMS instrument, align its optical beampath and test its performance. The protocol further provides instructions on how to prepare test samples of fluorescent beads, operate this instrument to acquire images of whole cells and how to analyse the raw image data to reconstruct super-resolution 3D data sets. Furthermore, we provide a trouble-shooting guide and present examples of anticipated results. An experienced optical instrument builder will require approximately 12 months from the start of ordering hardware components to acquiring high-quality biological images.Optical overview. The microscope presented here is centred around two opposing 100X/1.35 NA silicone oil immersion objective lenses (Olympus, UPLSAPO 100XS), OBJ0 and OBJ1 in Figure 1. Critically, these objectives must have closely matched magnification (within 0.3%) to allow for alignment of the two imaged fields of view for interference. Each objective lens is immediately followed by a quarterwave plate (Figure 1a, QWP0-1) set at 45 degrees with respect to the plane of the setup 2,4 . The quarterwave plates ensure that the emitted light is split in both beam paths into s-and p-polarisation components of equal intensity, independent of the initial polarisation orientation. Each objective's back pupil plane is imaged onto a deformable mirror (Figure 1a, lenses L1 and L3 for Objective OBJ0 and lenses L2 and L4 for OBJ1). The deformable mirrors (DMs) serve three functions: 1) introduce astigmatism to assist in emitter z-position determination, 2) correct for system aberrations