The present invention comprises a process for preparing water-dispersible single-chain polymeric nanoparticles, which comprises cross-linking a polymer having a solubility equal to or higher than 100 mg per litre of water, and an amount of complementary reactive groups comprised from 5 to 60 molar % of the total amount of monomer units present in the polymer chain; with a crosslinking agent having crosslinkable groups; at a temperature comprised from 20 to 25° C. in the absence of a catalyst; to obtain water-dispersible conjugates and compositions containing the nanoparticle; and the use thereof.