The present disclosure relates to a method for manufacturing a covalently functionalized coated magnetic nanoparticle and to said particles and uses thereof. The preparation method includes forming a shell of a hydrophilic polymer coating layer on top of a magnetic metal core coated with a carbon coating. In the method a particle comprising a magnetic metal core coated with a carbon coating is provided. The surface of the particle is subjected to covalent functionalization by generating amino reactive groups via diazonium chemistry and subsequently an irreversible attachment of an atom transfer radical polymerization (ATRP) initiator is carried out on said surface. A hydrophilic polymer layer is formed) by a surface initiated atom transfer radical polymerization (SI-ATRP) reaction with a monomer comprising N-isopropylacrylamide (NIPAM).