A Self-Activating Cyclic Amplification Near-Infrared Sonoafterglow Probe for High-Contrast Imaging In Vivo

Afterglow luminescence offers a promising strategy for ultrasensitive bioimaging by eliminating tissue autofluorescence and providing a high signal-to-background ratio (SBR). However, afterglow probes face several limitations, including limited luminescence brightness, short half-life, imperfect luminescent mechanisms, and reliance on preirradiation with low-penetration light. Herein, we develop a novel self-activating cyclic amplification near-infrared (NIR) sonoafterglow nanoprobe (3SCe-NP) based on a rationally engineered bis(diarylethenyl)terthiophene scaffold, which demonstrates an ∼270-fold enhancement in afterglow intensity and a 7-fold extension in half-life compared to the commonly used 2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV). The probe functions as an integrated single-molecule entity unifying the roles of a highly efficient sonosensitizer and an NIR afterglow emitter, which overcomes the drawbacks of weak afterglow brightness, complex fabrication, and poor reproducibility inherent in multicomponent systems. Furthermore, compared to previously reported single-reactive-site afterglow systems, the multireactive-site architecture of 3SCe-NP enables more extensive interactions with self-generated, multitype reactive oxygen species (ROS), creating a high density of chemical defects. This results in dramatically enhanced energy storage capacity and, consequently, a greatly intensified and sustained NIR afterglow upon ultrasound stimulation. Additionally, we uncovered a unique self-amplification mechanism that facilitates sustained ROS generation even after ultrasound cessation, thereby establishing a cyclic oxidation process that overcomes the constraint of conventional consumable afterglow probes relying on a single, depletable ROS. This nanoprobe achieves a high SBR, deep-tissue penetration, and rechargeable capability for longitudinal tumor imaging in vivo. We further demonstrated its utility by constructing an activatable sonoafterglow probe for monitoring immunotherapy responses, offering a useful tool for biomedical imaging.