The invention relates to the preparation and application of 20-150nm metallic nanoparticulate vesicles for photothermal anti-cancer therapy. The vesicles comprise metallic nanoparticles covalently bound to a hydrophilic and hydrophobic polymer. The preparation method generally entails dispersing a polymer-bound metallic nanoparticle in an organic solvent, adding an aqueous solution with a dispersing aid, sonicating the mixture, and finally removing the organic solvent until the vesicle forms. The final vesicle is stable wherein the metallic nanoparticle is covalently bound to the hydrophobic and hydrophilic polymer. By way of a non-limiting example, an exemplary vesicles can be one made from gold nanorods coated with polyethylene glycol and polylactic-co-glycolic acid (AuNR@PEG/PLGA) in an oil-in-water emulsion.