Gold nanoparticles in the range of 5 to 100nm in diameter were synthesized by simply tuning the concentration of aqueous poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer solution. As the copolymer concentration increased, the surface plasma resonance (SPR) of gold nanoparticles red-shifted and became more symmetrical. At the same time the gold nanoparticles became smaller and more uniform in size. Dissipative particle dynamics simulations indicated that PEO-PPO-PEO block copolymers formed micelles on the surface of particles, providing a protective layer to stabilizing them. Formation of uniform, small and stable gold nano-particles required that the copolymer be able to form micelles and that the core of the latter be hydrophobic. (c) 2007 Elsevier Ltd. All rights reserved.