X-ray recharged long afterglow luminescent nanoparticles MgGeO3:Mn2+,Yb3+,Li+ in the first and second biological windows for long-term bioimaging

In this paper, we have designed long afterglow luminescent MgGeO₃:Mn²⁺,Yb³⁺,Li⁺ (MGO) nanoparticles in the first (NIR-I) and second (NIR-II) biological windows. Yb³⁺ ions served not only as the trap center to enhance the NIR-I long afterglow emission of Mn²⁺ at 680 nm, but also as an emitting center to produce a NIR-II long afterglow emission at ∼1000 nm. Furthermore, we have found the addition of Li⁺ can greatly increase the NIR-II afterglow emission of Yb³⁺ and the optimal amount of Mn²⁺, Yb³⁺ and Li⁺ was found to be 0.1, 0.5 and 0.5 mol%, respectively. The MGO nanoparticles synthesized using sol-gel methods showed a uniform morphology with a diameter of 50-100 nm, which were suitable for applications in bioimaging. More importantly, we have found MGO nanoparticles can be effectively excited to produce long persistent NIR-I and II luminescence using soft X-rays, suggesting that low dosage soft X-rays can also serve as a more powerful and deep tissue excitation source to recharge MGO nanoparticles. Furthermore, the MGO nanoparticles can also be re-excited to produce photo-stimulated emission under the irradiation of 650 and 808 nm NIR lasers. The in vivo imaging results have shown that MGO nanoparticles modified with folic acid (FA) can effectively realize super long-term targeted in vivo imaging of inflammation with a high sensitivity via recharging using soft X-rays and NIR lasers, which can provide not only an accurate diagnosis of inflammation, but also long-term monitoring of possible changes in the focus of inflammation in real time.