An ultra-low detection limit gold(III) probe based on rhodamine-covalent hydrogel sensor.

A highly sensitive and selective optical chemosensor () for determination of Au was prepared by covalent immobilization of rhodamine ethylenediamine on agarose gel. Spectrophotometric studies of complex formation, chemical structures and purity of the hydrogel sensor were carried out using TGA, NMR, TEM, and IR. The complexation study results indicated that this probe can selectively detect Au via a metal ion chelation-induced ring-opening reaction, and then caused a remarkable colour change from colourless to pink and a strong fluorescence enhancement. Theoretical DFT calculation results suggested that the hydrogel sensor formed stable complexes with Au through a large number of cation-dipole interactions. Reusability has been established by repeatedly dipping and rinsing the hydrogel in aqueous Au and EDTA in basic solutions. We believe that this approach may provide an easily measurable and inherently sensitive method for Au detection in environmental and biological applications.