Gold nanoparticles (AuNPs) coated with ester-headed or ether-headed PEG ligands were synthesized. Ester-headed AuNPs, but not ether-headed, were transferred from the organic phase (CH2Cl2) to the alkali aqueous phase, indicating that the hydrolysis of the ester moiety triggered the phase transfer of the AuNPs. We found that AuNPs with ester-headed ligands (ester-AuNPs) were internalized into HeLa cells at a greater level than were ether-headed AuNPs.