β-Cyclodextrin stabilized gold nanoclusters (β-CD@AuNCs) as a signal-off fluorescent platform for Fe³⁺ ions detection

Herein, a facile synthetic approach for β-cyclodextrin (β-CD) stabilized fluorescent gold nanoclusters (AuNCs) has been introduced. The β-CD@AuNCs are uniformly monodispersed, possess an ultrasmall average size of 1.95 nm, and exhibit strong emission (450 nm, 12.09 ns lifetime). Intriguingly, ferric ions (Fe³⁺) effectively diminish the emission intensity of β-CD@AuNCs through an inner filter effect (IFE) process, owing to the notable overlap of the absorption spectrum of Fe³⁺ ions with the excitation spectrum of β-CD@AuNCs. This quenching enables the establishment of a signal-off platform for the sensitive and selective determination of Fe³⁺ ions. The developed platform exhibits a linear quenching response to Fe³⁺ concentrations from 0.20 to 400.0 µM (R² = 0.995) with a low LOD (80.0 nM), surpassing the U.S. Environmental Protection Agency's limit for drinking water (≈ 5.5 µM). Furthermore, this probe demonstrates an excellent selectivity among several metal ions. Based on these promising features, this sensing platform is successfully applied for the assay of Fe³⁺ ions in diverse environmental water samples and medicinal iron supplement tablets.