Fig. 1

Transmission electron microscopy (TEM) of microparticles (MPs). Micrographs show the negative staining of a typical sample observed by the TEM. a White particles of different sizes ranging from a few nanometers to 1 mm were present. As expected, all particles appeared as white structures in the dark background, due to phosphotungstic acid (PTA) negative staining. They were round-shaped and sometimes superimposed. This observation suggests that the smallest nanoparticles and MPs coexist in our sample, because it is well-known that MP size ranges from 100 to 1000 nm. b Two MPs of about 500 nm in diameter are shown, together with their measured diameters. (Images from Miranda F. PhD Thesis)