A novel fluorescent sensor for imaging of viscosity and ClO^- in plant cells and zebrafish

Viscosity and hypochlorite (ClO^-) are two crucial microenvironmental species that play significant roles in biological activities. Their abnormal levels are closely associated with numerous common diseases. Therefore, accurate and real-time detection of hypochlorite and viscosity related to inflammatory microenvironment conduces to elucidate the pathogenesis and further diagnose the disease. In this work, based on the strategy of the phenothiazine (PTZ)-dicyanoisophorone (DCO) dyad system, a new dual-response fluorescent sensor (PBI) was successfully constructed for the simultaneous detection and visualization of viscosity and hypochlorite (ClO^-) both in vitro and in vivo. The free sensor emits weak fluorescence in aqueous solution thanks to twisted intramolecular charge transfer (TICT) and photoinduced electron transfer (PET). However, in a high-viscosity system, the fluorescence emission of the sensor at 459 nm was significantly enhanced. Upon introduction of ClO^- in aqueous buffer solution, the PBI exhibited apparent fluorescence enhancement at 577 nm, and showed large Stokes shift (177 nm). The fluorescence responsive mechanism was confirmed using HRMS, ¹H NMR and DFT calculation analysis. Onion and lotus root cells imaging of PBI towards ClO^- was implemented. Furthermore, PBI has been successfully applied to the fluorescence imaging of viscosity and exogenous/endogenous hypochlorite in zebrafish.