A sensitive and selective sensor for oxidized glutathione (GSSG) detection based on the recovered fluorescence of naphthalimide-DPA (NDPA)-Fe 3 O 4 @SiO 2 -Cu(II) system is reported. NDPA-Fe 3 O 4 @SiO 2 was characterized by X-ray power diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR) and fluorophotometry. The fluorescence of NDPA-Fe 3 O 4 @SiO 2 could be quenched by Cu 2+ due to the coordination of Cu 2+ with the tridentate receptor DPA. This coordination process reduced the electron-donating ability of the nitrogen atom in the DPA moiety, thus suppressing the internal charge transfer (ICT) process in NDPA-Fe 3 O 4 @SiO 2 . In the presence of GSSG, the fluorescence of NDPA-Fe 3 O 4 @SiO 2 -Cu(II) was recovered because of strong coordination of Cu 2+ with GSSG, which promoted the decomplexation between NDPA-Fe 3 O 4 @SiO 2 and Cu 2+ , and enhanced the ICT process. The NDPA-Fe 3 O 4 @SiO 2 -Cu(II) nanomaterial exhibited high sensitivity towards GSSG, and a good linear relationship was obtained from 5nM to 60μM. The limit of detection, based on a signal-to-noise ratio of 3, was 50pM. In addition, the presence of magnetic Fe 3 O 4 nanoparticles (NPs) in NDPA-Fe 3 O 4 @SiO 2 NPs would also facilitate the magnetic separation of NDPA-Fe 3 O 4 @SiO 2 from the solution. Through the use of added internal standards, we successfully determined the concentration of GSSG in HEK 293 cell lysate to be 1.15μM by the prepared chemsensor NDPA-Fe 3 O 4 @SiO 2 -Cu(II). The proposed method is anticipated to fabricate other sensitive fluorescence sensors based on organic–inorganic hybrid magnetic nanoparticles.