A two-photon fluorescent probe for exogenous and endogenous superoxide anion imaging in vitro and in vivo

• A simple and efficient two-photon excited fluorescent probe for the real-time detection and imaging of O2
• − in living organisms.
• Using probe to visualize endogenously generated superoxide anion in inflamed lung.
• A potent and practical tool to study superoxide anion in various biological and pathological processes.

Herein, we report a novel quinoline derivative-based two-photon fluorescent probe 6-(dimethylamino)quinoline-2-benzothiazoline (HQ), which is capable of tracking superoxide anion in organisms with specific “turn-on” fluorescence response based on extension of π-conjugations and moderate ICT process. The probe exhibited favorable photophysical properties, a broad linear range and high photostability. It can specifically detect superoxide anion with a significant fluorescence enhancement and great linearity from 0 to 500 μM in PBS buffer. Furthermore, HQ shows low cytotoxicity and excellent photostability toward living cells and organisms, which was able to monitor endogenous superoxide anion fluxes in living cells and in vivo. For the first time, endogenous superoxide anion in lung inflammation was visualized successfully by using HQ through two-photon microscopy, and the probe HQ shows great potential for fast in-situ detecting of inflammatory response in live organisms.