X‑ray-activated near-infrared persistent luminescent probe for deep-tissue and renewable in vivo bioimaging

Near-infrared (NIR) persistent luminescence nanoparticles (PLNPs) are considered as new alternative optical probes due to being free of autofluorescence, benefited from the self-sustained emission after excitation and high signal-to-noise ratio. However, the NIR-emitted PLNPs always present a short decay time and require excitation by ultraviolet or visible light with a short penetrable depth, remarkably hindering their applications for in vivo long-term tracking and imaging. Therefore, it is important to develop NIR-emitted PLNPs with in vivo activation nature by new excitation sources with deeper penetrating depths. Here, we propose a new type of X-ray-activated ZnGa2O4:Cr PLNPs (X-PLNPs) with efficient NIR persistent emission and rechargeable activation features, in which both the excitation and emission possess a high penetrable nature in vivo. These X-PLNPs exhibit long-lasting, up to 6 h, NIR emission at 700 nm after the stoppage of the X-ray excitation source. More importantly, the designed X-PLNPs can be readily reactivated by a soft X-ray excitation source with low excitation power (45 kVp, 0.5 mA) to restore in vivo bioimaging signals even at 20 mm depth. Renewable in vivo whole-body bioimaging was also successfully achieved via intravenous injection/oral administration of X-PLNPs after in situ X-ray activation. This is the first time that NIR-emitted PLNPs have been demonstrated to be recharged by X-ray light for deep-tissue in vivo bioimaging, which paves the way for in vivo renewable bioimaging using PLNPs and makes the PLNPs more competitive in bioimaging area.