Size‐Dependent Blue Emission from Europium‐Doped Strontium Fluoride Nanoscintillators for X‐Ray‐Activated Photodynamic Therapy

Successful implementation of X‐ray‐activated photodynamic therapy (X‐PDT) is challenging because most photosensitizers (PSs) absorb light in the blue region, but few nanoscintillators produce efficient blue scintillation. Here, efficient blue‐emitting SrF 2 :Eu scintillating nanoparticles (ScNPs) are developed. The optimized synthesis conditions result in cubic nanoparticles with ≈32 nm diameter and blue emission at 416 nm. Coating them with the meso‐tetra( n ‐methyl‐4‐pyridyl) porphyrin (TMPyP) in a core–shell structure (SrF@TMPyP) results in maximum singlet oxygen ( 1 O 2 ) generation upon X‐ray irradiation for nanoparticles with 6TMPyP depositions (SrF@6TMPyP). The 1 O 2 generation is directly proportional to the dose, does not vary in the low‐energy X‐ray range (48–160 kVp), but is 21% higher when irradiated with low‐energy X‐rays than irradiations with higher energy gamma rays. In the clonogenic assay, cancer cells treated with SrF@6TMPyP and exposed to X‐rays present a significantly reduced survival fraction compared to the controls. The SrF 2 :Eu ScNPs and their conjugates stand out as tunable nanoplatforms for X‐PDT due to the efficient blue emission from the SrF 2 :Eu cores; the ability to adjust the scintillation emission in terms of color and intensity by controlling the nanoparticle size; the efficient 1 O 2 production when conjugated to a PS and the efficacy of killing cancer cells.