We report a strategy for the realization of NMR chemosensors based on the spontaneous self-assembly of lower rim pyridinium-functionalized tetraphopshonate cavitands on commercial silica nanoparticles. These nanohybrids enable the selective detection of physiologically relevant N-methylated amines, with a limit of detection of 31 μM, via STD-based NMR experiments, achieving for the first time fine structural selectivity in nanoparticle-assisted NMR chemosensing.