Characterization of nanoparticles with solid-state NMR spectroscopy and heteronuclear Overhauser enhancement spectroscopy (HOESY). a) ssNMR spectroscopy: Spin-lattice relaxation time, T1, of freeze-dried nanoparticles, and of nanoparticles swollen with water reveals that water is present inside the nanoparticle (same batch of nanoparticles as used for SANS measurements in Figure 4d). b,c) HOESY NMR of PFCE-loaded nanoparticles (NPs prepared without gadoteridol, PFCE-content 26 wt%, Rh(173°) = 97 nm) and nanocapsules (PFCE-content 14 wt%, Rh(173°) = 82 nm) with TFA (δ = −76 ppm (CF3‒COOH)) as internal reference show that in nanoparticles 19F of PFCE is close to water.