Transmission Electron Microscopy as a Powerful Tool to Investigate the Interaction of Nanoparticles with Subcellular Structures

Abstract

Nanomedical research necessarily involves the study of the interactions between nanoparticulates and the biological environment. Transmission electron microscopy has proven to be a powerful tool in providing information about nanoparticle uptake, biodistribution and relationships with cell and tissue components, thanks to its high resolution. This article aims to overview the transmission electron microscopy techniques used to explore the impact of nanoconstructs on biological systems, highlighting the functional value of ultrastructural morphology, histochemistry and microanalysis as well as their fundamental contribution to the advancement of nanomedicine.

Keywords: correlative microscopy; histochemistry; microanalysis; nanomedicine; nanoparticle biodistribution; nanoparticle uptake; ultrastructure.

Figure 1

Transmission electron micrographs of cells incubated for 24 h with different types of nanoparticulates (arrows): iron-based nanoparticles in adipose tissue stem cells (a), poly(lactic-co-glycolic acid) nanoparticles in C2C12 cells (b) and liposomes in HeLa cells (c). All cell samples were fixed with aldehydes, post-fixed with osmium tetroxide, embedded in epoxy resin and stained with uranyl acetate to enhance the image contrast. Note the low electron density of the polymeric nanoparticle in (b) that makes it hardly detectable in the intracellular milieu. Conversely, the intrinsic electron density of iron (a) and the binding of osmium tetroxide to the lipid components of liposomes (c) make the particulates in (a,c) clearly recognizable inside the cell. Bars: 200 nm.

Figure 2

Transmission electron micrographs of B50 cells incubated for 24 h with chitosan-based nanoparticles (asterisks). The sample in (a) was fixed with aldehydes, post-fixed with osmium tetroxide and embedded in epoxy resin and the sample in (b) was fixed with aldehydes, submitted to DAB photooxidation, post-fixed with osmium tetroxide and embedded in epoxy resin. Both samples were stained with uranyl acetate. In (a), the nanoparticle inside the endosome is hardly recognizable due to its weak contrast whereas in (b), the electron-dense reaction product of DAB photooxidation makes the nanoparticles clearly visible. Bars: 500 nm. Image in (b) from Malatesta et al. [161].

Figure 3

Transmission electron micrographs of C2C12 cells incubated for 2 h with hyaluronic acid-based nanoparticles (arrows). The sample in (a) was fixed with aldehydes, post-fixed with osmium tetroxide and embedded in epoxy resin and the sample in (b) was fixed with aldehydes, submitted to Alcian blue staining, post-fixed with osmium tetroxide and embedded in epoxy resin. Note the low electron density of the nanoparticles in the conventionally processed sample (a) and their increased visibility after the Alcian blue staining (b). Bars: 200 nm. Images from Carton et al. [90].