Compatible Fluorescent-Afterglow Luminescent Probe Enables Quantification of Photochemical Reaction-Driven Tumor Theranostics

In activatable tumor photodynamic therapy (PDT), developing imaging techniques that can continuously quantify the entire therapy treatment, including photosensitizer activation and 1O2 generation, is essential for visualization of cancer diagnostics and therapy prediction. As the imaging modes that respectively occur during and after light excitation, fluorescence (FL) and afterglow (AF) imaging are the best choices for consecutive visualizing of the entire PDT treatment. However, because the absorbed excitation energy is constant, the fluorescence and afterglow generation in a single chromophore through the radiative and non-radiative transition pathway are always competitive, which greatly thwarts the development of compatible FL/AF dual-mode probes. Herein, we developed an energy balance strategy between fluorescence and afterglow by transforming oxygen-substituted hemicyanine (OHD) into sulfur-substituted hemicyanine (SHD) to develop high-performance FL/AF dual-mode imaging molecular scaffolds. Based on the optimized scaffold, we reported an aminopeptidase N (APN) activatable probe (SHD-APN) for quantitative visualization of PDT with high sensitivity both in vitro and in vivo. More importantly, the activation of photosensitizer and generation of 1O2 can be consecutively visualized through fluorescence and afterglow imaging, respectively, so that the initial time, light intensity, and duration in PDT treatment can be accurately quantified in real-time. Besides, the established correlation between FL/AF intensity and photodynamic therapeutic efficacy will provide an opportunity to noninvasively guide precise treatment plans and achieve more effective treatment outcomes. Thus, this study not only presents strategies for quantitatively controlling of tumor PDT, but also provides a promising FL/AF scaffold for imaging of other disease evaluation.