A distinctive mitochondrion-targeting, in situ-activatable near-infrared fluorescent probe for visualizing sulfur dioxide derivatives and their fluctuations in vivo

Abstract

Sulfur dioxide derivatives are intimately involved in some physiological processes in organisms, and high levels of these substances can cause many diseases. Herein, we rationally prepared a mitochondrion-targeting, in situ-activatable near-infrared (NIR) fluorescent probe (DCQN) by coupling 2-(3,5,5-trimethylcyclohex-2-enylidene)malononitrile with 3-quinolinium carboxaldehyde. DCQN displayed a NIR fluorescence turn-on signal to indicate the presence of HSO₃⁻, along with a considerable hyperchromic shift from light yellow to purple via a 1,4-nucleophilic addition reaction. We were able to use DCQN to instantaneously and quantitatively determine the concentration of HSO₃⁻ with high specificity, a low detection limit (24 nM), a large Stokes shift (∼110 nm), and a high contrast ratio. Moreover, DCQN displayed good mitochondrion-targeting abilities and was in situ-activated by HSO₃⁻ to produce NIR fluorescence for imaging HSO₃⁻ in the mitochondria of live breast cancer cells. Furthermore, DCQN was used to monitor HSO₃⁻ in zebrafish with a high contrast ratio.