Acid-responsive mediated entropy driven signal amplification nanosystem for sensitive imaging of APE1 activity in living cells

Sensitive imaging of intracellular apurinic/apyrimidinic endonuclease 1 (APE1) activity is helpful to understand its physiological function and pathological role. Herein, an acid-responsive mediated entropy-driven signal amplification all-in-one nanosystem was proposed for sensitive imaging of APE1 activity in living cells. The nanosystem was constructed by modifying recognition probe, entropy-driven reaction (EDR) substrate and acidresponsive components on gold nanoparticles (AuNPs). After the nanosystem was endocytosed into the cell, the triplex in the acid-responsive components folded in the lysosome to free its complementary fuel strand. In the presence of APE1, it specifically cleaved the apurinic/apyrimidinic (AP) site in the recognition probe and released the EDR trigger. With the action of EDR trigger, EDR substrate and fuel strand, the EDR was completed and accompanied by the separation of fluorophore and quenching group in EDR substrate, resulting in obvious fluorescence signal recovery. The nanosystem successfully achieved sensitive imaging of APE1 activity in human cervical cancer cells (Hela cells), human breast cancer cells (MCF-7 cells) and human normal colonic epithelial cells (NCM460 cells) and monitored the changes of APE1 activity in Hela cells. The nanosystem provides a reliable approach for intracellular APE1 analysis and related biomedical research.