Rechargeable and LED-activated ZnGa 2 O 4  : Cr 3+ near-infrared persistent luminescence nanoprobes for background-free biodetection.

Persistent luminescence nanoparticles (PLNPs) have shown great promise in the field of biomedicine, but are currently limited by the challenge in the synthesis of high-quality PLNPs with bright persistent luminescence and a long afterglow time. Herein, we report a facile strategy for the synthesis of monodisperse, rechargeable and LED-activated ZnGa ₂ O ₄  : Cr ³⁺ near-infrared (NIR) PLNPs based on a modified solvothermal liquid-solid-solution method. The as-synthesized PLNPs are not only flexible for bioconjugation, but could also circumvent the limitation of the weak persistent luminescence and short afterglow time that most PLNPs confronted owing to their rechargeable capability. It was unraveled that both thermal activation and quantum tunneling mechanisms contributed to the afterglow decay of the PLNPs, and the quantum tunneling was found to dictate the LED-activated afterglow intensity and lasting time. Furthermore, by utilizing the superior excitation-free persistent luminescence, we demonstrated for the first time the application of biotinylated ZnGa ₂ O ₄  : Cr ³⁺ PLNPs as background-free luminescent nano-bioprobes for sensitive and specific detection of avidin in a heterogeneous assay with a limit of detection down to ∼150 pM, thus revealing the great potential of these NIR PLNPs in ultrasensitive biodetection and bioimaging.