An indole–based near–infrared fluorescent “Turn–On” probe for H2O2: Selective detection and ultrasensitive imaging of zebrafish gallbladder

Fluorescent probes play essential roles in medical imaging, where the researchers can select one of many molecules to use to help monitor the status of living systems under investigation. To date, a few scaffolds that allow the in vivo detection of H2O2 are available only. Herein, we provide a highly sensitive and selective near-infrared fluorescent probe that detects H2O2 based on the ICT sensing mechanism. We report the first indole–incorporated fluorescent probe Indo–H2O2 that allows H2O2 detection with a LOD of 25.2 nM featuring a boronate group conjugated to an indole scaffold; the boronate cleaves upon reaction with H2O2. A 5-membered malononitrile derivative was incorporated; Indo–H2O2 has near-infrared (NIR) properties and the reaction time is low (∼25 min) compared to other related probes. Indo–H2O2 was successfully employed in both endogenous and exogenous imaging trials of H2O2 in living cells. Indo–H2O2 also allows the real-time monitoring of H2O2 in vivo. It preferentially accesses the gallbladder of zebrafish. Our findings support Indo–H2O2 as a highly sensitive fluorescent NIR probe for detecting H2O2, and an idea to incorporate a central indole unit in future fluorescent probe designs.