NIR AIE System for Tracking Release of Taurine and ROS Scavenging

Fluorophores with aggregation-induced emission (AIE) feature are favorable tools for both chemical sensing and bioimaging. Inflammatory cells excessively express hydrolytic enzymes (esterase, protease and phosphatase) and are usually exposed to elevated levels of reactive oxygen species (ROS). Overexpression of ROS and the insufficient neutralization by antioxidants may give rise to the development of oxidative stress and chronic inflammation. Taurine (2-aminoethanesulfonic acid), as an effective antioxidant, can protect tissues from oxidative stress associated with various inflammatory diseases. Moreover, it has been recently reported that the incorporation of taurine can amazingly boost the cellular uptake for intracellular accumulation. Herein, we designed and synthesized a new near-infrared (NIR) AIE fluorophore DTPE. We anticipate that, the combination of the hydrophilic taurine with the NIR AIE fluorophore through an ester bond could be a remarkable method for extending the applications of AIE-active fluorophores e.g. as a trackable visualized therapeutic system featuring both imaging esterase-activated taurine release and ROS scavenging. Then we obtained the AIE probe system DTPE-Tau by incorporating taurine with the fluorophore through carbamate bond. The hydrophilic taurine moiety endows the system with enhanced water solubility and cellular uptake ability. The system is characterized by several advantages, such as large Stokes shift (225 nm), low cytotoxicity, and good photostability. The ester bond can be hydrolysed by the overexpressed esterase in inflammatory cells, thereby releasing a taurine moiety for ROS scavenging and in the meantime the AIE fluorophore moiety acts as a reporter for tracking esterase-activated taurine release. The enhancement of emission could serve as the reporting signal. The release rate is determined to be 75% for esterase at 0.05 mg/mL, calculated based on the fluorescence-intensity working curve. Also, the probe has been successfully utilized for tracking esterase-activated release of taurine and scavenging intracellular ROS in RAW264.7 cell line, which shows great potential for trackable visualized therapy.