Rotational-echo double-resonance (REDOR) C-13{F-19} and N-15{F-19} NMR spectra have been obtained for guest-host complexes of 6-fluorotryptophan and 4-(trifluoromethyl)benzophenone with polymeric amphiphilic nanoparticles, consisting of a polystyrene core covalently attached to a poly(acrylic acid)-co-[N-15]polyacrylamide shell. The REDOR spectra were used both to determine the composition of the nanoparticles and to find the locations of the fluorinated guests. Each guest resides near the core-shell interface of the nanoparticle, with the hydrophobic 4-(trifluoromethyl)benzophenone within the core and the amphiphilic 6-fluorotryptophan within the shell.