Rhodamine-Gold Hybrid Nanosensor for Rapid and Selective Detection of Hg²⁺ Ions in Environmental Samples

This research focuses on the selective detection of Hg²⁺ ions using hybrid nanosensors composed of rhodamine building blocks linked to polyamine units of varying chain lengths to produce Rho1-Rho4, which were subsequently conjugated with thioctic acid (RT1-RT4) and attached to the surface of gold nanoparticles to create hybrid nanosensors (GRT1-GRT4) designed for detecting heavy metals. The chemical structures, purity, morphology, and chemical composition were characterized through XRD, NMR, TEM, ATR-FTIR, and mass spectrometry. These hybrid nanosensors demonstrated excellent selectivity and sensitivity in colorimetric and fluorescence responses towards Hg²⁺, outperforming other metal ions. In their spirolactam form, the sensors were non-fluorescent but transformed into a fluorescent form upon interaction with Hg²⁺, resulting in enhanced fluorescence and colorimetric changes. Theoretical calculations indicated that Hg²⁺ could form stable complexes with the RT1 sensor by binding to the oxygen and nitrogen atoms in the spirolactam structure, as well as coordinating with the oxygen atom of the amide bond. The detection limit (LOD) was 1.68×10^-7 M with a response time of less than 40 seconds. This method offers a simple and highly sensitive approach for detecting Hg²⁺ ions in both environmental and biological applications, as confirmed by the characterization and experimental data.