A novel naphthalimide-based fluorescent probe with an ortho-hydroxybenzoquinone-fused pyrazine ring for highly sensitive and selective detection of ClO- in living cells.

Hypochlorite (ClO-) is an essential reactive oxygen species (ROS) in biological systems, but its abnormal concentration is closely associated with various diseases. Herein, we report a novel, highly sensitive and selective fluorescent probe, NPOH, based on an N-butyl-1,8-naphthalimide skeleton fused with an ortho-hydroxybenzoquinone-substituted pyrazine ring. Upon oxidation by ClO-, the amine group featuring an isopropyl substituent on the pyrazine ring is transformed into a positively charged quaternary ammonium cation via the intramolecular charge transfer (ICT) mechanism. Simultaneously, the ortho-hydroxyl group on the benzoquinone converts to a ketone form, resulting in a remarkable fluorescence enhancement (turn-on response). The probe NPOH exhibits high selectivity towards ClO- over other relevant reactive species, a fast response time, and a remarkably low detection limit of 6.67 nM. Furthermore, owing to its low cytotoxicity and excellent cell permeability, NPOH was successfully employed as a robust imaging tool to monitor both exogenous ClO- and the endogenous ClO- burst in living cells stimulated by MPO/H2O2, demonstrating its great potential for practical biological applications.