Naphthalamide-biotin-based fluorescent probe: A sensitive tool for CO detection in cancer cells and zebrafish

A fluorescent assay to detect carbon monoxide (CO), one of the signaling molecules in biological systems, was developed using a naphthalamide-biotin-based probe (EW5). The probe exhibited no significant fluorescence in phosphate-buffered saline/dimethyl sulfoxide solution. However, the fluorescence intensity of EW5 gradually increased at 533 nm with increasing concentrations of tricarbonyldichlororuthenium(II) dimer (CORM-2), a source of CO. Other possible competing analytes, such as Na⁺, K⁺, Fe²⁺, Zn²⁺, Cl⁻, NO₃⁻, HS⁻, cysteine, homocysteine, glutathione, H₂O₂, O₂^{. −}, NO, t-BuOOH, NaOCl, and formaldehyde, exhibited no significant effect on the probe's emission intensity. Moreover, EW5's fluorescence intensity rapidly escalated, achieving equilibrium swiftly within 10 min, indicative of a prompt and effective response to carbon monoxide (CO). Additionally, EW5 demonstrated commendable photostability following 60 min of uninterrupted exposure to light. The data reveal that EW5 can discern CO presence in aqueous buffers, cancerous and living cells, as well as in zebrafish, with remarkable selectivity and steadfastness. It is distinctly present in lysosomes and mitochondria, offering a viable real-time marker for probing CO-related reactions in biological settings.