The synthesis and properties of two responsive magnetoluminescent iron oxide nanoparticles for dual detection of DNA by MRI and luminescence spectroscopy are presented. These magnetoluminescent agents consist of iron oxide nanoparticles conjugated with metallointercalators via a polyethylene glycol linker. Two metallointercalators were investigated: Ru(bpy′)(phen) (dppz), which turns on upon DNA intercalation, and Eu-DOTA-Phen, which turns off. The characteristic light-switch responses of the metallointercalators are not affected by the iron oxide nanoparticles; upon binding to DNA the luminescence of the ruthenium complexes increases by ca. 20-fold, whereas that of the europium complex is >95% quenched. Additionally, the 17-20 nm magnetite cores, having permeable PEG coatings and stable dopamide anchors, render the two constructs efficient responsive contrast agents for MRI with unbound longitudinal and transverse relaxivities of 12.4-9.2 and 135-128 mM -1Fes-1, respectively. Intercalation of the metal complexes in DNA results in the formation of large clusters of nanoparticles with a resultant decrease of both r1 and r2 by 32-63% and 24-38%, respectively. The potential application of these responsive magnetoluminescent assemblies and their reversible catch-and-release properties for the purification of DNA is presented.