A rapid and selective phenothiazine-derived fluorescent probe for hypochlorous acid monitoring in living systems: from cellular imaging to in vivo systemic inflammatory response syndrome visualization.

Hypochlorous acid (HClO) is a pivotal constituent of the reactive oxygen species (ROS) family, playing a pivotal role in physiological processes such as immune defence and cellular signalling. However, it is important to note that excessive hypochlorous acid production is closely associated with various pathological conditions, including inflammation, neurodegenerative diseases, and cancer. Consequently, the development of tools capable of real-time, highly selective, and sensitive detection of HClO in biological systems is imperative for enhancing our comprehension of its mechanisms in life processes and facilitating early diagnosis of related diseases. The present study has designed and synthesised a novel small-molecule fluorescent probe, namely (E)-3-(2-(10-ethyl-10H-phenothiazin- 3-yl)vinyl)-1-methylquinoxalin-2(1H)-one), based on the ICT mechanism. The probe demonstrates a rapid response time (within 15 s), high selectivity, and a substantial Stokes shift (175 nm). It has been demonstrated that Probe QP is capable of detecting HClO at a concentration as low as 4 nM. Experiments conducted on cell experiments and zebrafish models have substantiated its capacity for fluorescence imaging of HClO, accompanied by its remarkable biosafety profile. These findings augur well for its potential applications in bioanalytical and biosensing domains. Mouse imaging demonstrated a strong correlation between HClO levels and systemic inflammatory response syndrome (SIRS) pathological processes. This probe facilitates dynamic visualization of SIRS progression and possesses considerable potential as a diagnostic instrument for inflammation-related diseases.