In vitro method for detecting luminescence variation, comprising: a) a step in which a physico-chemical disturbance is applied on a particle used as a probe; in which the physico-chemical disturbance is applied on the particle by electromagnetic radiation, X-rays, radiation due to a magnetic field, a pH variation, and/or a temperature variation; said particle comprising at least one ferrimagnetic or ferromagnetic iron oxide nanoparticle associated with at least one compound, wherein the nanoparticle is not bound to the compound by at least one nucleic acid or by at least one amino acid, wherein said compound dissociates from the iron oxide nanoparticle, wherein the dissociation of the compound does not lead to its destruction, as a result of said physicochemical perturbation applied on the particle, wherein the physicochemical perturbation induces a dissociation of the weak bond between said compound and said nanoparticle, said compound being a luminescent substance that possesses at least one chemical function selected from the group consisting of carboxylic acid, phosphoric, sulfonic, ester, amide, ketone, alcohol, phenol, thiol, amine, ether, sulfide, acid anhydride, acyl halide, amidine, nitrile, hydroperoxide, imine, aldehyde, peroxide and having at least one luminescence property which varies upon dissociation between said nanoparticle and said compound; then b) a step for detecting the luminescence variation of said particle used as a probe. a) a step in which a physico-chemical disturbance is applied on a particle used as a probe; in which the physico-chemical disturbance is applied on the particle by electromagnetic radiation, X-rays, radiation due to a magnetic field, a pH variation, and/or a temperature variation; said particle comprising at least one ferrimagnetic or ferromagnetic iron oxide nanoparticle associated with at least one compound, wherein the nanoparticle is not bound to the compound by at least one nucleic acid or by at least one amino acid, wherein said compound dissociates from the iron oxide nanoparticle, wherein the dissociation of the compound does not lead to its destruction, as a result of said physicochemical perturbation applied on the particle, wherein the physicochemical perturbation induces a dissociation of the weak bond between said compound and said nanoparticle, said compound being a luminescent substance that possesses at least one chemical function selected from the group consisting of carboxylic acid, phosphoric, sulfonic, ester, amide, ketone, alcohol, phenol, thiol, amine, ether, sulfide, acid anhydride, acyl halide, amidine, nitrile, hydroperoxide, imine, aldehyde, peroxide and having at least one luminescence property which varies upon dissociation between said nanoparticle and said compound; then in which the physico-chemical disturbance is applied on the particle by electromagnetic radiation, X-rays, radiation due to a magnetic field, a pH variation, and/or a temperature variation; said particle comprising at least one ferrimagnetic or ferromagnetic iron oxide nanoparticle associated with at least one compound, wherein the nanoparticle is not bound to the compound by at least one nucleic acid or by at least one amino acid, wherein said compound dissociates from the iron oxide nanoparticle, wherein the dissociation of the compound does not lead to its destruction, as a result of said physicochemical perturbation applied on the particle, wherein the physicochemical perturbation induces a dissociation of the weak bond between said compound and said nanoparticle, said compound being a luminescent substance that possesses at least one chemical function selected from the group consisting of carboxylic acid, phosphoric, sulfonic, ester, amide, ketone, alcohol, phenol, thiol, amine, ether, sulfide, acid anhydride, acyl halide, amidine, nitrile, hydroperoxide, imine, aldehyde, peroxide and having at least one luminescence property which varies upon dissociation between said nanoparticle and said compound; then b) a step for detecting the luminescence variation of said particle used as a probe.