Designing zeolites for medical applications is a challenging task that requires introducing new functionalities without altering the intrinsic properties such as morphology, crystallinity, colloidal stability, surface charge, and porosity. Herein, we present the encapsulation of luminescent ruthenium-tris(2,2'-bipyridyl) complex in faujasite (FAU) zeolite nanocrystals (Ru(bpy)(3)-FAU) and their use as an intracellular localization tracer. Upon exciting the Ru(bpy)(3)-FAU zeolite at 450 nm, the sample gives rise to an orangered emission at 628 nm, thus permitting its use for cellular imaging and localization of the zeolite nanoparticles. The nanosized Ru(bpy)(3)-FAU zeolite is characterized in terms of size, charge, crystallinity, morphology, porosity, thermal stability, and sorption capacity. The potential toxicity of Ru(bpy)(3)-FAU on U251-MG glioblastoma cells was evaluated. A safe concentration (50-100 mu g/ml) for the Ru(bpy)(3)-FAU zeolite is identified. The luminescent properties of the ruthenium complex confined in the zeolite nanocrystals allow their localization in the U251-MG cells with a main accumulation in the cytoplasm. The Ru(bpy)(3)-FAU nanosized zeolite is a potential candidate for biological applications for being stable, safe, capable of loading respiratory gases, and easily probed in the cells owing to its luminescent properties. (C) 2020 Elsevier Inc. All rights reserved.