Abstract: The present invention relates to conjugates having colloidal stability in a medium which comprises a nanoparticle NP, a plurality of linkers of formula (II) comprising a sulfonyl moiety or a phosphonyl moiety as defined herein, and a plurality of groups A attached to the linkers, wherein: NP is a gold, silver or platinum nanoparticle; with the condition that an amount equal to or higher than 50% of the linkers of formula (II) are in ionic form when the conjugate is in an aqueous medium. It also relates to a process for the preparation of these conjugates and to pharmaceutical compositions containing them. The conjugates of the invention are used for the treatment of cancer.