Nanoparticle passivation by molecular recognition moieties (small molecules, aptamers, antibodies) imputes unique characteristics to nanoparticles (NPs) and unlocks their fascinating selectivity to targeting disease sites. Although non-passivated nanomaterials may archive selective targeting by exploring NP features and their interaction with biofluids proteins, such studies are scarce in the literature. Here, we report spherical manganese-based carbonaceous NPs (MnCQD), which specifically target mice kidneys after intravenous injection, even without direct surface chemical modification. Also, the NPs provide high image contrast in T1 magnetic resonance imaging (MRI) with subtle toxicological effects. The unexpected selectivity of MnCQD to the kidney has been examined based on their determined intrinsic properties and their interaction with two blood proteins: Bovine Serum Albumin (BSA), and Human Transferrin (HTF). More particularly, aspects such as size, composition, superficial charge, spectroscopic features, interaction mechanism, affinities, thermodynamic, and protein structural changes have been investigated. All these results highlight the excellent potential of MnCQD as a low toxic T1-MRI contrast agent and open the prospect of using non-functionalized NPs as a selective agent to target specific organs.