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Magnetic iron oxide nanoparticles (IONPs) are under investigation for several biomedical applications,[1] including drug delivery,[2] magnetic resonance imaging (MRI),[3] and hyperthermia therapy.[4] Indeed, the application of an external alternating magnetic field (AMF) to IONPs induces production of thermal energy, by Neel and/or Brownian relaxation, that can be used to generate local heating for tumor repression.[4, 5] IONPs have been also proposed as controlled delivery systems in which remote release of suitable therapeutic agents is stimulated by the heat generated upon AMF exposure.[5, 6] In the design of ligands that allow simple and efficient functionalization of IONPs with a desired moiety, cycloaddition reactions are ideal candidates. Cycloadditions have received broad attention because these orthogonal clicktype reactions can be efficiently used for bioconjugation.[7] Additionally, cycloadditions are chemoselective and may be efficiently performed under physiological conditions, both invitro and invivo.[7] The 1, 3-dipolar azide–alkyne click reaction has found widespread applications in materials science and bioconjugation, as either copper-catalyzed (CuAAC) or strain-promoted azide–alkyne cycloaddition.[8] The Diels–Alder (DA) reaction is known as a thermoreversible reaction between diene and alkene derivatives (dienophiles) to form cycloadducts in a clean and simple click reaction that is effective in aqueous conditions.[9] Owing to these desirable features, both cycloadditions have been widely employed in a variety of materials synthesis applications, including IONP functionalization.[1, 8, 10, 11] While IONPs have been …