Cryo-Correlative Light and Electron Microscopy at High Resolution of Large Volumes

Light microscopy (LM) and electron microscopy (EM) each have their advantages for investigating biological problems. LM has benefited enormously from the development of genetically encoded probes which hijack cellular machinery to tag proteins of interest within cells and tissue. However, LM is insensitive to non-fluorescent components and lacks the ability to precisely resolve the intricate structure of biology. On the other hand, EM has exquisite nanometer resolution and global contrast but cannot to pin-point specific proteins. Here I describe the instrument we have developed to perform 3D multi-color super-resolution fluorescence microscopy on high pressure frozen biological specimens at helium temperatures (< 10K). Cryo-fixation avoids chemical fixation artifacts and allows the sample to be prepared optimally for both LM and EM. Super-resolution is necessary to bridge the resolution gap between LM and EM. Ultracold temperatures allow new photophysics to be exploited. By combining our microscope with large-volume (100 µm linear dimension), high-resolution (8 nm) FIB-SEM we can precisely place proteins of interest within the overall cellular context and allow new biological questions to be addressed.