A Water-Soluble Turn-on Fluorescent Probe for Detection and Plant Bioimaging of Al3+ and As3+ Ions

An imidazolium salt (E)-3-(hydroxy-4-(((2-hydroxyphenyl) imino) methyl) benzyl)-1-methyl-1 H-imidazol-3-ium chloride (HBIm) is synthesized and evaluated for its fluorescence behavior toward metal ions. The probe detected Al³⁺ and As³⁺ ions when excited at 326 nm in an aqueous medium. The nonfluorescent HBIm exhibited a “turn-on” fluorescence response upon being treated with Al³⁺ (λ_em = 510 nm) and As³⁺ (λ_em = 499 nm) ions due to the chelation-enhanced fluorescence effect. The detection limits for Al³⁺ and As³⁺ are low and are found to be 0.38 and 2.37 nM, respectively. Furthermore, the binding constants for these ions are significantly high, 1.59 × 10⁵ M⁻¹ for Al³⁺ and 3.54 × 10⁴ M⁻¹ for As³⁺. The binding mechanism between HBIm and Al³⁺ and As³⁺ ions is supported by various techniques, including ESI-MS, Job's plot, ¹H NMR, X-ray photoelectron spectroscopy, SEM-EDS, and density functional theory studies. The reversibility experiments are conducted using EDTA ions to develop the corresponding logic gates. HBIm has the potential to detect Al³⁺ and As³⁺ ions in real samples, such as plant cells, tissues, and water samples.