Visualizing cellular G-quadruplexes with a bioinspired chemiluminescent probe

Fluorescence imaging of G-quadruplexes (G4s) is fundamentally limited by autofluorescence and phototoxicity from external excitation. Chemiluminescence, which generates light internally via chemical reaction, offers a promising solution. Here, we report the first chemiluminescent probe, PCL, for selective G4 visualization in vitro and in cells. PCL conjugates the high-affinity G4 ligand PhenDC3 with a reactive oxygen species (ROS)-activatable imidazopyrazinium chemilumophore. Crucially, we demonstrate that PCL's excitation-free mechanism enables high-contrast, low-background imaging of G4s in living cells. This work establishes a novel chemiluminescent paradigm for visualizing G4s with minimal perturbation.