A conjugate having colloidal stability in a medium which comprises a nanoparticle NP, a plurality of linkers of formula attached to the nanoparticle, and a plurality of groups A attached to the linkers, wherein: NP is a gold, silver or platinum nanoparticle; n represents 0 or 1; wherein: when n is 0, the linker of formula is attached to the nanoparticle NP through one sulfur atom; and when n is 1, the linker of formula is attached to the nanoparticle NP through two sulfur atoms; p represents a value selected from 1 to 3; and X represents a (C 2 -C 20)hydrocarbon chain, or a (C 2 -C 20)hydrocarbon chain wherein at least one carbon atom is replaced by a carbonyl group or a heteroatom selected from the group consisting of O and N; and wherein these (C 2 -C 20)hydrocarbon chains are optionally substituted with one or more substituents selected from the group consisting of halogen, OH, CONH 2, CO 2 (C 1 -C 6)alkyl and -CHO; ---- is either absent or alternatively represents a single bond; wherein: when ---- is absent, Y is either a sulfonyl moiety of formula (i), or alternatively a phosphonyl moiety of formula (ii): and when ---- is a single bond, Y is either a sulfonyl moiety of formula (i'), or alternatively a phosphonyl moiety of formula (ii'), which is attached to A by the oxygen atom: the groups A are platinum biradicals independently selected from the group consisting of formula, formula, formula, and a pharmaceutically acceptable salt of any of them: wherein the platinum biradical is attached to two independent linker molecules of formula wherein ---- is a single bond, and Y is either a sulfonyl moiety of formula (i'), or alternatively a phosphonyl moiety of formula (ii'), through the oxygen atom of the moiety of formula (i') or (ii'); with the condition that an amount equal to or higher than 50% of the linkers of formula are in ionic form when the conjugate is in an aqueous medium. NP is a gold, silver or platinum nanoparticle; n represents 0 or 1; wherein: when n is 0, the linker of formula is attached to the nanoparticle NP through one sulfur atom; and when n is 1, the linker of formula is attached to the nanoparticle NP through two sulfur atoms; p represents a value selected from 1 to 3; and X represents a (C 2 -C 20)hydrocarbon chain, or a (C 2 -C 20)hydrocarbon chain wherein at least one carbon atom is replaced by a carbonyl group or a heteroatom selected from the group consisting of O and N; and wherein these (C 2 -C 20)hydrocarbon chains are optionally substituted with one or more substituents selected from the group consisting of halogen, OH, CONH 2, CO 2 (C 1 -C 6)alkyl and -CHO; ---- is either absent or alternatively represents a single bond; wherein: when ---- is absent, Y is either a sulfonyl moiety of formula (i), or alternatively a phosphonyl moiety of formula (ii): and when ---- is a single bond, Y is either a sulfonyl moiety of formula (i'), or alternatively a phosphonyl moiety of formula (ii'), which is attached to A by the oxygen atom: when ---- is absent, Y is either a sulfonyl moiety of formula (i), or alternatively a phosphonyl moiety of formula (ii): and when ---- is a single bond, Y is either a sulfonyl moiety of formula (i'), or alternatively a phosphonyl moiety of formula (ii'), which is attached to A by the oxygen atom: the groups A are platinum biradicals independently selected from the group consisting of formula, formula, formula, and a pharmaceutically acceptable salt of any of them: wherein the platinum biradical is attached to two independent linker molecules of formula wherein ---- is a single bond, and Y is either a sulfonyl moiety of formula (i'), or alternatively a phosphonyl moiety of formula (ii'), through the oxygen atom of the moiety of formula (i') or (ii'); with the condition that an amount equal to or higher than 50% of the linkers of formula are in ionic form when the conjugate is in an aqueous medium.