Colorimetric Dual Sensors of Metal Ions Based on 1,2,3-Triazole-4,5-Dicarboxylic Acid-Functionalized Gold Nanoparticles

A simple, rapid, selective, and cost-effective colorimetric assay for Cr³⁺ and Eu³⁺ ion detection has been developed using functionalized gold nanoparticles. Gold nanoparticles (AuNPs) were prepared using HAuCl₄, where sodium citrate is a reducing agent as well as a capping agent, and then functionalized with 1,2,3-triazole-4,5-dicarboxylic acid (TADA). Fourier transform infrared (FTIR) and Raman spectroscopies suggested that TADA was functionalized on the surface of AuNPs through the N atom of triazole. The TADA-functionalized gold nanoparticles (TADA@AuNPs) simultaneously detect Cr³⁺ and Eu³⁺ ions from aqueous solution and showed different responses to the two metal ions (Cr³⁺ and Eu³⁺) based on an aggregation-induced color change of AuNPs. They showed a color change from wine red to blue, which was easily detected by the naked eye, as well as by UV-visible and FTIR spectroscopies. The surface plasmon resonance absorbances of Cr³⁺ and Eu³⁺ are 633 and 671 nm, respectively, when Cr³⁺ and Eu³⁺ react with TADA@AuNPs and showed good linearity with Cr³⁺ and Eu³⁺ concentrations with detection limits 5.89 nM and 4.30 μM, respectively (S/N = 3). The TADA@AuNPs showed excellent selectivity toward Cr³⁺ and Eu³⁺ compared to those of the 16 different metal ions. We had also tested the selectivity of TADA@AuNPs toward Eu³⁺ compared to that of the other 10 lanthanide systems. Optimal detection was achieved toward Cr³⁺ and Eu³⁺ ions in the pH range 4-10. In addition, TADA@AuNPs were applied to detect Cr³⁺ and Eu³⁺ ions from lake water showing low interference.