Fig. 1. Schematic illustration of (A) Atto647N–Tf NP synthesis, (B) characterization by HAADF-STEM and (C) HAADF-STEM image and single particle-level EDXS elementary maps showing the distribution of oxygen (O-Kα1 line – blue), nitrogen (N-Kα1 line – red) and sulfur (S-Kα1 line – green) within the NP. (D) Histogram of Atto647N–Tf NP size distribution measured based on STEM images; the blue line shows the corresponding Gaussian fit. The size analysis was carried out by using ImageJ software.