Electron microscopy observations were carried out at the LMA-INA-Universidad Zaragoza facilities. Scanning electron microscopy (SEM, Inspect F50; FEI, Eindhoven, the Netherlands) at an accelerating voltage of 10–15 kV was employed to determine the size (100 NPs were measured for performing the statistical analysis) and morphology of the synthesized NPs. The freshly prepared NPs were mixed during 1.5 hours with the same volume of phosphotungstic acid solution (7.5% w/v) used as contrast agent. The dispersion was centrifuged and washed three times with Milli-Q water and later resuspended. A drop of the resulting NP suspension was placed on a glass slide, dried in air, and coated with platinum under vacuum before SEM observation.
Transmission electron microscopy (TEM) observations were carried using a T20-FEI microscope with a LaB6 electron source fitted with a “SuperTwin®” (FEI Company, Hillsboro, OR, USA) objective lens allowing a point-to-point resolution of 2.4 Å. Approximately 2.5 μL suspension of stained PLGA NPs was pipetted onto a transmission electron microscopy copper grid with a continuous carbon film. Samples were let to evaporate completely and then were analyzed.
Transmission electron microscopy (TEM) observations were carried using a T20-FEI microscope with a LaB6 electron source fitted with a “SuperTwin®” (FEI Company, Hillsboro, OR, USA) objective lens allowing a point-to-point resolution of 2.4 Å. Approximately 2.5 μL suspension of stained PLGA NPs was pipetted onto a transmission electron microscopy copper grid with a continuous carbon film. Samples were let to evaporate completely and then were analyzed.