Fig. 2

A variety of different microscopic methods used to visualize blank LPNs (a1–a4) and CS-PLGA NPs (b1–b4). a1, b1 SEM images show a smooth, spherical morphology of the nanoparticles, a2, b2 TEM images of particles without staining give a hint about the core–shell structure, seen in a dark electron dense layer surrounding a brighter core. a3, b3 To emphasis this structure and increase the contrast, the particles were stained with 0.5% wt/V PTA and imaged with TEM and further unstained nanoparticles were visualized with a less harsh method using Cryo-TEM with red arrows pointing to the particles (a4, b4). Scanning electron microscopy (SEM), transmission electron microscopy (TEM)