LAUSR

Spatially resolved imaging of intracellular pH during ischemic stroke (IS) is critical for demarcating salvageable penumbral tissue and tracking lesion progression; however, engineering IS-specific pH sensors remains challenging. Herein, we engineered an apurinic/apyrimidinic endonuclease 1 (APE1)-activatable ratiometric DNA nanosensor (LPF) by encapsulating a dual-strand DNA probe (PF) within liposomes. The PF probe operates through a dual-strand molecular switch: the i-motif in the cytosine-rich F-strand undergoes pH-dependent folding, activating Cy3/Cy5 FRET for ratiometric pH sensing; simultaneously, the AP site on the P-strand blocks pH-sensing activity until cleaved by cytoplasmic APE1 upregulated in IS lesions, thereby enabling IS-specific activation. Liposomes enhance delivery to ischemic cells. In vitro studies identified 30-nt and 18-nt P-strand as optimal for protection and activation, respectively, with PF exhibiting high APE1 selectivity under acidic conditions. Confocal imaging demonstrated LPF's capability to specifically monitor pH changes in oxygen-glucose-deprived (OGD) cells, requiring cytoplasmic APE1 upregulation for activation. In MCAO mice, LPF achieved enzyme-mediated IS-specific activation and dynamically tracked pH gradients. This work establishes the first APE1-activated ratiometric nanosensor for spatially precise pH imaging in IS, providing a platform for stroke diagnosis and personalized intervention.