A Pd2+-Free Near-Infrared Fluorescent Probe Based on Allyl Ether Isomerization for Tracking CORM-3 with High Contrast Imaging in Living Systems

As a CO donor, CORM-3 is widely used nowadays to study the role of CO as a gasotransmitter and potential drug in biological systems. Developing methods to detect CORM-3 in live systems will contribute to these studies. Herein, we developed a novel Pd2+-free near-infrared fluorescent probe CORM3-AE for detecting CORM-3 both in live cells and in vivo. We found that the allyl ether group in CORM3-AE could be cleaved by CORM-3 directly via an isomerization process to release the NIR fluorophore QCy7 and cause distinct NIR fluorescence changes. Importantly, CORM3-AE responds quickly and shows high sensitivity and selectivity for CORM-3 with NIR fluorescence turn-on changes at 743 nm (λex = 662 nm), and when the excitation wavelength is 450 nm, CORM3-AE can respond to CORM-3 with ratiometric fluorescence signals at 743/605 nm. Moreover, CORM3-AE can track CORM-3 in live cells and animals with excellent imaging performance. Thus, this work not only provides a powerful new tool for CORM-3 detection in live systems but also provides a new method to construct CORM-3 probes by allyl ether isomerization.