Chromium-doped zinc gallate: Impact of Sn4+ co-doping on the persistent luminescence properties at the nanoscale applied to bio-imaging

Persistent luminescence (PersL) nanoparticles emit a signal that lasts long after the excitation has ended, enabling highly sensitive bioimaging without background noise. By using UV light as the excitation source prior to injection, a strong PersL signal can be detected in vivo before disappearing within a few hours. For long-term imaging, we have shown in the past that visible LED can be used to re-excite ZnGa1.995Cr0.005O4 (ZGO:Cr3+) nanoparticles in vivo, producing a signal intensity that is, however, much lower compared to the signal obtained after the UV pre-excitation method. This lower signal intensity of the nanoprobe when using a visible LED may prevent its detection in some cases. Herein, we report an improvement in visible LED excitation efficiency using PersL Zn1.33Ga1.335Cr0.005Sn0.33O4 (ZGSO:Cr3+) nanoparticles. We fully compared ZGSO:Cr3+ and the original ZGO:Cr nanoparticles in terms of structure, optical properties and bio-imaging potential. Co-doping with tin strongly increases persistent luminescence, even at the nanoscale. In vivo imaging results showed that ZGSO:Cr3+ exhibited an approximately 3-fold signal enhancement over ZGO:Cr3+ using UV pre-excitation. More interestingly, when using LED excitation, the signal intensity of ZGSO: Cr3+ is more than 10 times higher than that of ZGO:Cr3+, making ZGSO nanoparticles much easier to detect. ZGSO:Cr nanoparticles can be surface-modified with PEG to produce nanoprobes with much longer residence time in blood. This unique comparison between the two compositions makes ZGSO:Cr3+ a more effective imaging diagnostic probe than the original ZGO:Cr3+ nanoparticles, opening up new applications for in vivo diagnostics.