Stable gold nanocolloids with controllable surface modification and functionalization

This paper demonstrates a new method for fabrication of stable gold nanoparticle-poly(ethylene glycol) (PEG) conjugates with a defined number of PEG molecules. The PEG molecules are directly bound to the surface of gold nanoparticles with almost 100% conjugation efficiency and the PEG surface coverage is tunable between values of 0 and 100%. Gold nanoparticles for the nanoparticle PEG conjugates are prepared by femtosecond laser ablation in liquid of a gold bulk target in deionized water. This method for fabrication of nanoparticles creates gold surfaces which are negatively charged and chemically clean. This facilitates uniform and controlled binding of thiolated PEG molecules to the surface of the gold nanoparticles. The method used to bind PEG to gold can be used with other biomolecules to prepare gold nanoparticles with single or mixed monolayers of biologically important molecules.