This Ph.D dissertation focused on the development of high performance magneto-fluorescent-conjugated nanoparticles, combining tunable II-VI quantum dots and surface modified-non-stoichiometric iron oxide nanoparticles, aiming application in non-destructive assays. Three types of iron oxide nanoparticles were synthesized as magnetic anchoring platforms. These materials were characterized by means of several techniques, and a new methodology of external weighting with analytical balances was developed to evaluate the saturation magnetization of the samples and to investigate the magnetophoretic process. The water-soluble quantum dots were obtained by means of kinetically controlled synthesis, which were monitored in real-time, providing a powerful technique in the investigation of synthetic pathways. The magneto-fluorescentconjugated nanoparticles were assembled by the appropriate combination of the constituents with surfactant species, acting as spacers in order to minimize the Förster Resonance Energy Transfer mechanisms (FRET). Such new probes were characterized by high resolution transmission electron microscopy, fluorescence and electronic spectroscopy, and by vibrating sample magnetometer, and were successfully tested in the in non-destructive assays for the detection of fractures in metallic structures.