Water-dispersible 2 nm FePt ultrasmall nanocrystals coated by a biocompatible triblock copolymer, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEO-PPO-PEO) were directly synthesized in a single-step nanoemulsion process. The FTIR investigation proves the PEO-PPO-PEO molecules on the surface of the resulting nanocrystals, which render the nanocrystals hydrophilic for aqueous dispersion without using conventional ligand exchange and offer proper protection of the nanocrystals from oxidation. The structural and morphological analysis reveals both single-crystallinity and high crystallinity of the nanocrystals in the face-centered cubic phase, with an excellent monosize distribution of 1.95 +/- 0.18 nm in diameter. Moreover, the polymer-capped nanocrystals possess well-defined magnetic behavior and the aqueous dispersion-collection process of the nanocrystals was demonstrated for application readiness of such ultrasmall nanocrystals in aqueous media. (c) 2011 Elsevier B.V. All rights reserved.