Cyclen-pyrene coupled fluorescent Indicator for selective detection of Sn2+ ions and its applications to bioimaging

A fluorescent probe based on cyclen-pyrene, named 2,2′-(7,10-bis(pyren-1-ylmethyl)-1,4,7,10-tetraazacyclododecane-1,4-diyl)diacetic acid (L), was effectively developed for the sensitive and selective detection of Sn²⁺ in ethanol/HEPES buffer (5 mM, pH 7.2, 1,9 v/v) solutions. The probe L shows a strong preference for the Sn²⁺ ion in the presence of other biologically relevant metal ions. Upon binding with Sn²⁺, L undergoes the CHEF effect and suppresses the PET process, resulting in a significant turn-on emission enhancement. The detection limit for Sn²⁺ was 7.71 nM, which meets the WHO's permissible concentration for Sn²⁺ in drinking water. The recognition mechanism of the L.Sn²⁺ complex was verified through FT-IR analysis, ¹H NMR titration, and DFT studies. Furthermore, ESI-MS spectral analysis confirmed a 1:1 binding stoichiometry. L has also been used to detect Sn²⁺ ions in real samples and to create a paper-based test kit for efficient monitoring of Sn²⁺ ions. Moreover, bioimaging studies demonstrated that L serves as a useful fluorescent marker for detecting Sn²⁺ in living cells and zebrafish.