Supplementary Table 2 At least 3 specimen grids were prepared for each condition examined. The present study incorporates a total of 262 tomograms.

NPnf: non-functionalized nanoparticles. n.s.: not shown, that is, representative figures not presented in the manuscript. ^†The 6.5 nm EB1-gold conjugate was frozen in liquid nitrogen and conserved at −80 °C before use. This experiment was performed to check whether the sample sustained freezing, since it was prepared in Rennes (France) and sent to Utrecht (Netherlands) for the TIRF experiments. ^∗Microtubules were assembled in the presence of GTP, EB1-gold 9.8 nm 200 nM, using centrosomes as nucleation templates. EB1-gold comets were observed at the plus ends of centrosome-nucleated microtubules, in agreement with the observations made on GMPCPP-MT seed nucleated microtubules.