Figure 3.

Scanning transmission electron microscopy–annular dark field (STEM-ADF) image of a typical polyplex and energy dispersive X-ray (EDX) spectra obtained from the red boxes (1) and (2). Both spectra show carbon, nitrogen, and oxygen as the main constituents. Smaller amounts of sodium, chlorine, sulfur, and calcium can be detected due to residuals of the buffer solution. Importantly, a significant amount of phosphorous can only be detected for area 1. In addition, the relative nitrogen content is considerably lower for area 1.