In this feature article, gold nanoparticle Conjugates loaded with phthalocyanine-based PDT drugs are prepared and tested for delivery efficiency and PDT efficacy oil HeLa cancer cells. It could be shown that the delivery and PDT outcome are strongly affected by the bond that links the drug load to the nanoparticle Surface. Whereas labile amino adsorption to the An nanoparticle surface allows for efficient drug release into the cancer cells and for efficient PDT, a covalent thiol bond to the An nanoparticle leads to the delivery of the drug into cell vesicles, and no PDT effect is observed. This work highlights the importance of carefully choosing the interaction between drug molecules and the nanoparticle surface.