Thiospirolactone as a recognition site: Rhodamine B-based fluorescent probe for imaging hypochlorous acid generated in human neutrophil cells

A rhodamine B thiospirolactone-based probe, compound 1, namely 3′,6′-bis(diethylamino)-3H-spiro[2-benzothiophene-1,9′-xanthene]-3-one, has been successfully developed as a highly sensitive and selective fluorescent probe for imaging hypochlorous acid generated in human neutrophil cells. The probe was found to display "Off–On" switching in its fluorogenic and chromogenic responses to HClO and this was suggested to result from the hypochlorous acid-induced thio-spiro ring opening. This probe displayed excellent performance in high sensitivity, good selectivity for hypochlorous acid over other reactive oxygen species in biological pH condition, rapid reactivity as well as high tolerance to autoxidation under light. The probe has been successfully applied to detect HClO generated in living human neutrophil cells, implying the probe might be a new efficient tool in detecting the roles of hypochlorous acid in biological systems.