Wash-free super-resolution sensing of telomeric G-quadruplex/t-loop states in living cells using a cyclometalated Ir(III) probe

We present a fluorogenic cyclometalated Ir(III) probe (cIr-Q) that selectively lights up telomeric G-quadruplexes (GQs), features a large Stokes shift (∼168 nm), high photostability, rapid passive nuclear entry (≤2 min), and wash-free operation. Integrated with super-resolution microscopy, cIr-Q enables in situ quantification of higher-order telomeric architectures in living cells. NMR and biochemical assays further delineate a TERRA-initiated pathway: RNA-DNA hybridization exposes the G-rich strand to fold into GQs that facilitate t-loop formation. In a senescence model, cIr-Q reports an aging-associated decrease of GQs/t-loop signals. These results establish cIr-Q as a practical biosensing platform for live-cell readout of telomeric structural biomarkers, bridging materials design with chromosome biology without fixation or permeabilization.