A rapid, biocompatible turn-on NIR probe for ferrous ion imaging in living cells and zebrafish

Leveraging an ICT-controlled turn-on mechanism, we developed a near-infrared fluorescent probe (E)-2-bromo-4-(2-(4-(dicyanomethylene)-4H-chromen-2-yl)vinyl)-N,N-dimethylaniline oxide, hereinafter denoted as DCMB, built on a propanedinitrile-benzopyran scaffold for the specific detection of ferrous ions (Fe²⁺). The probe exhibits a remarkable fluorescence enhancement upon exposure to Fe²⁺, achieving a detection limit of 5.6 µM and a rapid response within 90 s. Strategic incorporation of bromine substituents extends the operational pH window to 5.0-7.5, outperforming most conventional indicators and ensuring robust performance in both physiological milieus and acidic tumor microenvironments. In addition, DCMB displays exceptional selectivity for Fe²⁺ over abundant biological metal ions (Ca²⁺, Mg²⁺, etc.) and potential interfering substances in biological systems, showing no significant effect. It is well-suited for detecting Fe²⁺ in complex biological matrices and has been successfully applied for imaging in living cells and zebrafish employed for in vivo.