Monolayer-protected nanoparticles provide a straightforward access to self-organized receptors that selectively bind different substrates in water. Molecules featuring different kinds of noncovalent interactions (namely, hydrophobic, ion pairing, and metal-ligand coordination) can be grafted on the nanoparticle surface to provide tailored binding sites for virtually any class of substrate. Not only the selectivity but also the strength of these interactions can be modulated. Such recognition ability can be exploited with new sensing protocols, based on NMR magnetization transfer and diffusion-ordered spectroscopy (DOSY), to detect and identify organic molecules in complex mixtures.