Synthesis and Characterization of 1 H-Imidazole-4,5-dicarboxylic Acid-Functionalized Silver Nanoparticles: Dual Colorimetric Sensors of Zn²⁺and Homocysteine

A colorimetric assay has been developed for Zn2+ and homocysteine (Hcy) detection using functionalized silver nanoparticles (AgNPs). AgNPs have been synthesized using silver nitrate, where sodium citrate is used as a stabilizing agent and NaBH4 as a reducing agent. Then, the nanoparticles (citrate@AgNPs) were functionalized with 1H-imidazole-4,5-dicarboxylic acid (IDCA). UV-visible and FTIR spectra suggested that IDCA was functionalized on the surface of citrate@AgNPs through the N atom of the imidazole ring. The IDCA-functionalized silver nanoparticles (IDCA@AgNPs) simultaneously detected Zn2+ and Hcy from aqueous solution and showed different responses to the two analytes (Zn2+ and Hcy) based on the aggregation-induced color change of IDCA@AgNPs. They showed the color change from yellow to red, which was easily discriminated by visual inspection as well as UV-visible spectroscopy. The surface plasmon resonance absorbance values of Zn2+ and Hcy are 485 and 512 nm, respectively, when Zn2+ and Hcy react with IDCA@AgNPs. IDCA@AgNPs showed linearity with Zn2+ and Hcy concentrations, with the detection limit of 2.38 μM and 0.54 nM, respectively (S/N = 3). The IDCA@AgNPs showed excellent selectivity toward Zn2+ and Hcy compared to the different metal ions and amino acids, respectively. Optimal detection was achieved toward Zn2+ and Hcy in the pH range 3-10. In addition, IDCA@AgNPs were used to detect Zn2+ and Hcy from lake water, showing low interference.