The authors report an electrochemical phenol biosensor based on the immobilization of laccase (Lac) on the surface of copper capped magnetic core-shell (Fe3O4-SiO2) nanoparticles (MNPs). After synthesis, MNP surfaces were functionalized by silanization and then, modified with histidine (His) and copper, respectively. The performance of the MNP-His/Cu/Lac biosensor has been investigated at -0.05V versus Ag/AgCl. The proposed biosensor allowed to detect catechol and phenol in the range of 0.01-0.4mM and 0.025-0.2mM, respectively. Finally, phenol analysis in culture medium of P. putida adapted to phenol was successfully demonstrated with appreciable recovery values.