The cryosectioning technique is an alternative method for preparing biological material for Transmission Electron Microscopy (TEM). We have applied this technique to study the mechanism of cell internalization of stimuli-responsive polymeric nanogels exploited as cargo nanovectors. With respect to conventional TEM processing, cryosectioning technique better preserves the morphology of solvent-sensitive nanogels and enhances the visibility of membrane-bounded organelles inside the cell cytoplasm. In this chapter we describe the protocols we have established to perform Electron Microscopy (EM)-immunocytochemistry, Electron Tomography (ET), and Energy Dispersive X-ray Spectroscopy (EDXS) chemical analysis in Scanning TEM (STEM) on cryosections of HeLa cells treated with pH-responsive nanogels hosting short interference RNA (siRNAs) and iron oxide nanoparticles (IONPs).