Dear Bruna, for confolcal and fluorescent microscopy and SEM I almost always use 37% formalin evaporations (if there is no fluorescent proteins in the cells): just expose microscopic glass slides with cells on them in a closed volume with 37% formalin (you can put a cotton piece dipped in formalin) for 10-15 min. I would also recommend to add ati-bleach reagents prior to fluorescent microscopy. If you are going to apply TEM, there seems to be no single way to prepare your samples because TEM samples need to be not only fixed but also dry and resin-embedded. Good luck! Lena

You can have a look at the paper:

Article Correlated fluorescence and 3D electron microscopy with high...

Briefly, yeast cells were high-pressure frozen, freeze substituted, and embedded in Lowicryl. 300 nm resin sections placed on EM grids were imaged in a Fluorescence Microscope prior to Electron Tomography.

"All yeast cultures were grown at 30°C until reaching log phase, pelleted by filtering, and cryo-immobilized by HPF with a high pressure freezing system (EM PACT2; Leica). All samples were further processed by freeze substitution (FS) and embedding in a temperature-controlling device (model AFS2; Leica). FS occurred at −90°C for 48–58 h with 0.1% (wt/vol) uranyl acetate in glass-distilled acetone. The temperature was then raised to −45°C (5°C/hour), and samples were washed with acetone and infiltrated with increasing concentrations (10, 25, 50, and 75%; 4 h each) of Lowicryl in acetone while the temperature was further raised to −25°C. 100% Lowicryl was exchanged three times in 10-h steps and samples were UV polymerized at −25°C for 48 h, after which the temperature was raised to 20°C (5°C/hour) and UV polymerization continued for 48 h. 300-nm sections were cut with a microtome (Ultracut UCT; Leica) and a diamond knife and picked up on carbon-coated 200 mesh copper grids. " (from Kukulski W et al. J Cell Biol 2011)