Rational Design of a Dual‐Reactivity‐Based Fluorescent Probe for Visualizing Intracellular HSNO

Thionitrous acid (HSNO), the smallest S‐nitrosothiol, is emerging as a potential key intermediate in cellular redox regulation linking two signaling molecules H₂S and NO. However, the chemical biology of HSNO remains poorly understood. A major hurdle is the lack of methods for selective detection of HSNO in biological systems. Herein, we report the rational design, synthesis, and evaluation of the first fluorescent probe TAP‐1 for HSNO detection. TAP‐1 showed high selectivity and sensitivity to HSNO in aqueous media and cells, providing a useful tool for understanding the functions of HSNO in biology.