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

A highly sensitive and selective optical chemosensor (Arg-Rhoen) for determination of Au³⁺ 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 Au³⁺ 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 Arg-Rhoen formed stable complexes with Au³⁺ through a large number of cation-dipole interactions. Reusability has been established by repeatedly dipping and rinsing the hydrogel in aqueous Au³⁺ and EDTA in basic solutions. We believe that this approach may provide an easily measurable and inherently sensitive method for Au³⁺ detection in environmental and biological applications.

Gold sensing with rhodamine immobilized hydrogel-based colorimetric sensor

A highly sensitive and selective optical membrane for determination of Au³⁺ was synthesized by immobilization of a rhodamine derivative on agarose hydrogel. The sensing dye was synthesized by solvatochromism of rhodamine B via rhodamine lactone-zwitterion equilibrium. UV-vis spectroscopy, scanning electron microscopy (SEM), thermal gravimetric analysis (TGA) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) were employed to confirm that the rhodamine-lactone (RhoL) was incorporated into the agarose hydrogel. The results showed that the sensor was highly selective for recognizing Au³⁺ over other metal ions in real systems. In addition, DFT calculation results suggested that the membrane sensor formed stable complexes with Au³⁺ through a large number of cation-dipole and ion-ion interactions. In addition, according to changes in signaling upon adding various Au³⁺ concentration, the limit of detection of Arg-RhoL for Au³⁺ is calculated to be 5 µM. This approach may provide an easily measurable and inherently sensitive method for Au³⁺ ion detection in environmental and biological applications.