Uniform　hydrophobic　nanoparticles　synthesized　in　nonpolar　solvents　possess　excellent　physio-chemical　properties,　showing　great　potential　in　biomedical　applications.　However,　the　presence　of　hydrophobic　ligands　on　their　surfaces　limits　their　use　under　physiological　conditions.　Inspired　by　protein　coronas　present　at　the　nano-bio　interface,　here　we　report　a　facile　and　universal　method　for　phase　transfer　and　surface　bioengineering　of　hydrophobic　nanoparticles　using　β-sheet-rich　silk　fibroin,　a　FDA-approved　natural　protein.　Due　to　its　amphiphilicity　and　high　mechanical　stiffness,　the　β-sheet-rich　silk　fibroin　not　only　readily　drags　nanoparticles　from　an　organic　phase　into　aqueous　media　but　also　endows　them　with　excellent　monodispersity　and　long-term　stability.　The　silk　fibroin-coated　nanoparticles　can　retain　the　magnetic　and　optical　properties　of　the　original　nanoparticles,　acting　effectively　as　probes　for　biomedical　imaging　and　biosensing.　Furthermore,　hydrophobic　drugs　can　be　easily　adsorbed　onto　the　protein　coating　via　hydrophobic　interaction,　allowing　the　construction　of　promising　theranostic　nanoagents.　Given　these　unique　features,　the　strategy　developed　here　possesses　great　promise　in　facilitating　biomedical　applications　of　hydrophobic　nanomaterials.　©　The　Royal　Society　of　Chemistry　2017.