A dual-function fluorescence 'turn-on' probe that allows Zn (II) bioimaging and quantification of water in the...

Herein, a Eugenol-derived fluorescence 'turn-on' probe FLHE was synthesized by condensing 2-((3-(trifluoromethyl)phenyl)amino)benzohydrazide with 5-allyl-2-hydroxy-3-methoxybenzaldehyde. FLHE demonstrated very low fluorescence in the studied organic solvents of varying polarities. However, upon titration with Zn²⁺ in HEPES buffer (pH = 7.4, 50% ACN, v/v), FLHE showed 40-fold higher fluorescence signals indicating the formation of the FLHE-Zn²⁺ complex. The fluorescence turn-on phenomenon upon FLHE-Zn²⁺ complex formation results from a chelation-enhanced fluorescence (CHEF) effect. The FLHE-Zn²⁺ complexation demonstrated a stokes shift of 156 nm (λ_ex = 350 nm, λ_em = 506 nm) and an about 33-fold increase in the quantum yield (FLHE, Φ = 0.007; FLHE-Zn²⁺ complex, Φ = 0.23). The binding constant (K_a) determined by the Benesi-Hildebrand plot for interaction between FLHE and Zn²⁺ was 5.33 × 10³ M^-1. FLHE demonstrated a LOD of 31.8 nM for detecting Zn²⁺ in the environmental samples without interference from other cations and anions. FLHE-based paper strip (FLHE-PS) assay was developed to quantify the Zn²⁺ ions in water and the water content of organic solvent. FLHE-PS allows the detection of Zn²⁺ in aqueous solutions with a LOD of 63.2 nM and quantifying water in acetonitrile with a LOD of 0.14%. These results indicate that the FLHE has high applicability for detecting Zn²⁺ in living cells and environmental samples and detecting the presence of water in the organic solvents.