Monolayer-protected nanoparticles provide an appealing artificial receptor scaffold for targeting proteins and related biomacromolecules. During the past two years, multiple efforts have focused on the engineering and application of nanoparticle-protein interactions. These investigations include the molecular recognition of proteins with nanoparticles in aqueous media, self-assembly of proteins and nanoparticles either in solution or on surface, and construction of nanoparticle-based protein sensors.