Adaptable coumarin-based fluorescent molecular multianalyte sensor for Zn²⁺, Hg²⁺ and Cu²⁺<i>via</i> different sensing modalities and its bioimaging applications

A new organic coumarin-based probe, DCMC, was successfully designed and synthesized. Characterization techniques such as single-crystal X-ray diffraction, ¹H-NMR, ¹³C-NMR, IR, and mass spectroscopy were used to analyse the chemical structure of this probe. Systematic sensing studies of DCMC in DMSO/H₂O (9/1, v/v, pH = 7.2) by fluorescence and absorption methods showed selectivity towards Hg²⁺, Zn²⁺ and Cu²⁺ by different sensing modalities. DCMC showed a distinctive red shift in UV-Vis spectra for Cu²⁺, while no similar response was observed for Hg²⁺ and Zn²⁺. Additionally, it showed significant fluorescence quenching towards Hg²⁺, and for Zn²⁺, an eminent ratiometric fluorescence response was observed. The detection limit of DCMC towards Hg²⁺ and Zn²⁺ was calculated and established to be in the order of 10^-9 (M), and for Cu²⁺, it was in the order of 10^-8 (M). A detailed investigation was performed on the detection mechanism using Job's plot, ¹H-NMR, ESI mass analysis and density functional theory (DFT) calculations, which established the 2 : 1 binding stoichiometry for all three ions. Further, a stability study was performed over a period of five days to establish the stability of DCMC prominently. The probe also coherently recognised the sensing cations in the solid state, making DCMC a portable kit for on-site detection. Besides, the live cell imaging study using the MCF-7 cell line to detect Zn²⁺ and Hg²⁺ revealed the detection capability of DCMC and its biocompatible nature. Finally, density functional theory and time-dependent density functional theory were implemented, which established the experimental outcomes theoretically.