Rare Earths-Doped and Ceria-Coated Strontium Aluminate Platelets─Versatile Luminescent Platforms for Correlated Lifetime Imaging by Multiphoton FLIM and PLIM

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Abstract
We report our recent advances in the design and synthesis of functional and hybrid composite nanomaterials with properties geared toward life sciences assays and as platforms for biomedical imaging applications. Using a stepwise reverse micelle procedure, we synthesized hybrid platelets comprising rare earth-doped strontium aluminate cores labeled Eu,Dy:SrAlO, where the phase nominally denoted as Sr0.95Eu0.02Dy0.03Al2O4 dominates the nature of the composite, as demonstrated by extensive X-ray diffraction investigations. These were coated with a biocompatible cerium oxide shell, giving rise to the hierarchical hybrids denoted CeO2@Eu,Dy:SrAlO. Such Eu/Dy codoped strontium aluminates exhibit broad luminescent emissions with high optical sensitivity. The CeO2 shell further imparts biocompatibility and water dispersibility, resulting in kinetically stable nanoplatelets which can translocate into living cells in lifetime imaging protocols that were optimized for imaging across nano- and microscales. Multiphoton fluorescence lifetime imaging microscopy (MP FLIM) confirmed the luminescent properties in thin films and living cellular environments. These nanohybrids represent a significant step forward in the development of functional molecules and materials, leveraging directed and self-assembly strategies for their synthesis. Their luminescence (detectable by fluorescence as well as phosphorescence emission intensity correlated with emission lifetime), negligible toxicity on the time scale of imaging assays and up to 72 h, and biocompatibility with cellular milieu enabled their tracing with living cells. Their cellular activity was estimated by standard MTT assays in PC-3 and provided a further insight into their behavior in biological environments. The inclusion of heavy cerium and strontium atoms enhanced X-ray attenuation, supporting multimodal imaging by integrating optical and X-ray-based methods, which paves the way for potential applications in computed tomography correlated to confocal microscopy coupled with fluorescence lifetime imaging. These findings highlight the versatility of these luminescent hybrids for bioimaging and as synthetic scaffolds toward nanomedicine applications, bridging advanced imaging modalities with functional materials design.
Funding Information
  • Engineering and Physical Sciences Research Council (EP/L016354/1)
  • European Research Council (617107, 963937)
  • Ministerio de Ciencia, Innovación y Universidades (TED2021-129876B-I00, TED2021132779B-100)
  • Agencia Estatal de Investigación (PID2019-104118RB-C21)
  • Biotechnology and Biological Sciences Research Council (BB/W019655/1)

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