Particle comprising: - at least one luminescent metal complex of formula [Ln]., wherein: - Ln is a lanthanide ion, - L is an organic ligand comprising a hydrophilic unit with at least 6 chelating groups chosen from the group consisting of hydroxyl, carboxyl, optionally in the carboxylate form, carbonyl, ether, phosphonate, phosphinate, thiolate, amino and imino functions, and - at least one drug comprising a conjugated aromatic system, wherein said drug is not covalently bonded to the metal complex, and wherein the drug is an anticancer agent, said particle having a size comprised from 3 nm to 2 000 nm, and wherein the distribution of the metal complex and the drug within the particle is such that the mean distance between a drug molecule and a metal complex is less than 15 nm, wherein said ligand is of formula: wherein: - R 1, R 2, R 3 and R 4 are independently selected from the group consisting of hydroxyl, carboxyl, optionally in the carboxylate form, carbonyl, ether, phosphonate, phosphinate, thiolate, amino and imino functions, - n 1, n 2, n 3 and n 4 are independently selected from 1 to 6, - n' and n" are independently selected from 1 to 6, and - A is a saturated, partially saturated or aromatic heterocycle, comprising at least one coordinating group of formula -N= or -N<, said heterocycle being optionally substituted by one or more lipophilic groups, or wherein said ligand is of formula: wherein: - R' 1, R' 2, R' 3 and R' 4 are independently selected from the group consisting of hydroxyl, carboxyl, optionally in the carboxylate form, carbonyl, ether, phosphonate, phosphinate, thiolate, amino and imino functions, - n' 1, n' 2 and n' 3 are independently selected from 1 to 6, - R' is selected from the group consisting of hydrogen, methyl, linear or branched C 2 -C 24 alkyl groups, and C 1 -C 24 fluoroalkyl groups, and - A' is a saturated tetraazacycloalkyl ring comprising from 6 to 12 carbon atoms. - at least one luminescent metal complex of formula [Ln]., wherein: - Ln is a lanthanide ion, - L is an organic ligand comprising a hydrophilic unit with at least 6 chelating groups chosen from the group consisting of hydroxyl, carboxyl, optionally in the carboxylate form, carbonyl, ether, phosphonate, phosphinate, thiolate, amino and imino functions, and - Ln is a lanthanide ion, - L is an organic ligand comprising a hydrophilic unit with at least 6 chelating groups chosen from the group consisting of hydroxyl, carboxyl, optionally in the carboxylate form, carbonyl, ether, phosphonate, phosphinate, thiolate, amino and imino functions, and - at least one drug comprising a conjugated aromatic system, wherein said drug is not covalently bonded to the metal complex, and wherein the drug is an anticancer agent, - R 1, R 2, R 3 and R 4 are independently selected from the group consisting of hydroxyl, carboxyl, optionally in the carboxylate form, carbonyl, ether, phosphonate, phosphinate, thiolate, amino and imino functions, - n 1, n 2, n 3 and n 4 are independently selected from 1 to 6, - n' and n" are independently selected from 1 to 6, and - A is a saturated, partially saturated or aromatic heterocycle, comprising at least one coordinating group of formula -N= or -N<, said heterocycle being optionally substituted by one or more lipophilic groups, - R' 1, R' 2, R' 3 and R' 4 are independently selected from the group consisting of hydroxyl, carboxyl, optionally in the carboxylate form, carbonyl, ether, phosphonate, phosphinate, thiolate, amino and imino functions, - n' 1, n' 2 and n' 3 are independently selected from 1 to 6, - R' is selected from the group consisting of hydrogen, methyl, linear or branched C 2 -C 24 alkyl groups, and C 1 -C 24 fluoroalkyl groups, and - A' is a saturated tetraazacycloalkyl ring comprising from 6 to 12 carbon atoms.