Selective dual-mode detection of reactive oxygen species and metal ions by chemodosimetric vs. chelation pathways: fluorescence ‘turn-on’ with OCl− and Zn2+/Mn2+, employing theoretical, practical, and bioimaging applications

Abstract

An indole-coupled diaminomaleonitrile-based fluorescent chemosensor IMA has been designed and developed for the selective detection of ROS (OCl⁻) and metal ions Zn²⁺ and Mn²⁺ via chemodosimetric and chelation pathways respectively. The selective sensing of OCl⁻ is induced by a method of oxidatively cleaving of the imine bond of IMA, forming free indole aldehyde, which results in a 21-fold enhancement of fluorescence at 521 nm, with a detection limit of 2.8 µM. On the other hand, the selective binding of IMA with Zn²⁺ and Mn²⁺ results in chelation-induced enhanced fluorescence (CHEF) and increased intermolecular charge transfer (ICT), leading to a 4-fold and 3-fold fluorescence enhancement at 432 nm and 435 nm, with the detection limits of 12.71 µM and 17.34 µM, respectively. UV-vis spectroscopy, fluorescence, DFT study, mass spectra, ¹H-NMR analysis, and Job's plot analysis have been used to validate the sensing mechanism of IMA with OCl⁻, Zn²⁺, and Mn²⁺. For practical applications, the binding of IMA with OCl⁻ has been utilized in the detection of commercial samples like bleaching powder and water analysis. Bio-imaging studies were conducted with IMA in the presence of OCl⁻ and Zn²⁺ using green gram seeds in a physiological medium.