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, we developed efficient blue-emitting SrF 2 :Eu scintillating nanoparticles. Our optimized synthesis conditions resulted in cubic nanoparticles with ∼ $\sim $ 32 nm diameter and blue emission at 416 nm. Coating them with the porphyrin TMPyP in a core-shell structure (SrF@TMPyP) resulted in maximum singlet oxygen ( 1 O 2 ) generation upon X-ray irradiation for nanoparticles with 6 TMPyP depositions (SrF@6TMPyP). The 1 O 2 generation was directly proportional to the dose, did not vary in the low energy X-ray range (48-160 kVp), but was 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 presented a significantly reduced survival fraction compared to the controls. The SrF 2 :Eu Scintillating nanoparticles (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. This article is protected by copyright. All rights reserved.