Abstract

Abstract Persistent luminescence (PerL) materials continue emitting light long after their excitation has stopped. Prepared in the form of nanoparticles they revealed their full potential as bio-nanoprobes for in vivo small animal imaging in the last 15 years. PerL materials enable to overcome the limitation of weak light penetration in living tissues. As such, they constitute remarkable light mediators to implement photodynamic therapy (PDT) in deep-seated tissues. This article reviews the recent achievements in PerL-mediated PDT in vitro as well as in small animal cancer models in vivo. PerL-mediated PDT is realized through the smart choice of a tandem of a PerL material and a photosensitizer (PS). The physical association of the PerL material and the PS as well as their targeting ability is debated. Implants or mesoporous nanoparticles emerge as particularly valuable cargos that further permit multimodality in imaging or therapy. The diversity of charge-trapping mechanisms in a few PerL materials enables a large versatility in the excitation protocols. Although the PerL agent can be pre-excited by UV light before its introduction into the animal, it also induces effective PDT after simple infrared or visible LED illumination across tissues as well as after a mild X-ray irradiation.

Highlights

  • Persistent luminescence (PerL) materials continue emitting light long after their excitation has stopped

  • Developed as nanoprobes enabling autofluorescence-free in vivo imaging in small animals, they have appeared in numerous examples of PerL-mediated photodynamic therapy (PDT)

  • In most of the reported examples, ZGO:Cr or ZGGO:Cr are used as the PerL material, which conveniently enables the double modality of PDT and PerL imaging

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Summary

Delivering light to the PSs in deep PDT

When light interacts with matter, i.e. here with living tissue, reflection, refraction, scattering and absorption take place and lead to beam attenuation. Most tissues will scatter light and highly pigmented areas will absorb it due to water, oxyhemoglobin, deoxyhemoglobin, melanin, and cytochromes. All possible ways of delivering light internally to the PS have been continuously explored by taking advantage of lighttransmitting devices, often at the cost of more invasiveness. Both these improvements are insufficient to tackle deep-seated lesions or metastasis. Alternative approaches consist into introducing molecules, nanoobjects or materials that can play the role of internal lights

Shifting the PS absorption efficiency towards the infrared
Indirect PDT: mediators for deep PDT
Energy transducers
Self-illuminating probes
Persistent luminescence mediators for PDT
Trapping and de-trapping mechanisms in PerL materials
Result
Application to PerL-mediated PDT
Findings
Conclusion and future directions
Full Text
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