Precise discrimination of G-quadruplex conformation by chiral nanoassembly with photo-reversibility.

The precise detection and dynamic modulation of G-quadruplexes (G4s) are essential for elucidating their roles in gene regulation, genome stability, and disease pathogenesis. However, seldom has a photo-reversible small-molecule assembly capable of dynamically responding to G4s been reported. Here, we present a novel self-assembly strategy based on a π-extended compound, S2, which spontaneously forms functionalized helical nanoassemblies with a 51-fold enhanced chiral signal. These nanoassemblies enable S2 to discriminate parallel, antiparallel, and hybrid G4 topologies through ratiometric fluorescence and stereoselective spatial alignment. Remarkably, the S2 nanoassembly also exhibits enhanced sensitivity for RNA G4s over existing probes. Mechanistic studies reveal that this superior performance arises from a cascade response mechanism involving "assembly disruption-monomer release-fluorescence activation". Moreover, the photoisomerization capability of S2 facilitates reversible binding to parallel G4s under alternating UV/Vis irradiation. Finally, S2 is successfully used for in situ imaging of RNA G4s in live cells and for the detection of RNA G4s in clinical blood samples, enabling the differentiation between healthy individuals and lung cancer patients. This study introduces a "nanoassembly-G4 interactome" framework that extends beyond traditional ligand design paradigms, offering a valuable tool for the analysis of G4s in both biological and clinical contexts.