Single-Stage Microfluidic Synthesis Route for BaGdF₅:Tb³⁺-Based Nanocomposite Materials: Synthesis, Characterization...

Rare-earth-doped nanoscaled BaGdF₅ is known as an efficient contrasting agent for X-ray micro-CT and NMR as well as a promising candidate for X-ray photodynamic therapy, thereby opening an opportunity for theragnostic applications. Conventional synthesis of Ln-doped BaGdF₅ consider a long-lasting batch procedure, while a conjugation with photosensitizer usually implies a separate stage requiring active mixing. To the best of our knowledge, in this work, we for the first time obtain BaGdF₅:Tb³⁺ nanophosphors in a microfluidic route at temperatures as low as 100 °C while decreasing the time of thermal treatment down to 6 min. The proposed synthesis route allows for the obtaining of single-phase and monodisperse BaGd_1-xF5:Tb_x³⁺ nanoparticles with an averaged particle size of ca. 7-9 nm and hydrodynamic radius around 22 nm, as estimated from TEM and DLS, respectively. In addition, X-ray-excited optical luminescence has been recorded in situ for the series of nanophosphors synthesis with varied flow rates of Tb³⁺ and Gd³⁺ stock solutions, thereby anticipating a possible application of microfluidics for screening a wide range of possible co-dopants and reaction conditions and its effect on the optical properties of the synthesized materials. Moreover, we demonstrated that BaGd_1-xF₅:Tb_x³⁺@RoseBengal conjugates might be obtained in a single-stage route by implementing an additional mixer at the synthesis outcome, namely, by mixing the resulting reaction mixture containing nanoparticles with an equivalent flow of photosensitizer aqueous solution. In vitro cytotoxicity test declares moderate toxicity effect on different cell lines, while the results of flow cytometry indirectly confirm cellular uptake. Finally, we report long-term biodistribution monitoring of the synthesized nanocomposites assessed by X-ray micro-CT in the in vivo experiments on balb/c mice, which depicts an unusual character of agents' accumulation.