Novel Carboxylic Acid-Capped Silver Nanoparticles as Antimicrobial and Colorimetric Sensing Agents

The present work reports the synthesis, characterization, and antimicrobial activities of adipic acid-capped silver nanoparticles (AgNPs@AA) and their utilization for selective detection of Hg²⁺ ions in an aqueous solution. The AgNPs were synthesized by the reduction of Ag⁺ ions with NaBH₄ followed by capping with adipic acid. Characterization of as-synthesized AgNPs@AA was carried out by different techniques, including UV-Visible spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Dynamic Light Scattering (DLS), and zeta potential (ZP). In the UV-Vis absorption spectrum, the characteristic absorption band for AgNPs was observed at 404 nm. The hydrodynamic size of as-synthesized AgNPs was found to be 30 ± 5.0 nm. ZP values (-35.5 ± 2.4 mV) showed that NPs possessed a negative charge due to carboxylate ions and were electrostatically stabilized. The AgNPs show potential antimicrobial activity against clinically isolated pathogens. These AgNPs were found to be selectively interacting with Hg²⁺ in an aqueous solution at various concentrations. A calibration curve was constructed by plotting concentration as abscissa and absorbance ratio (A_Control - A_Hg/A_Control) as ordinate. The linear range and limit of detection (LOD) of Hg²⁺ were 0.6-1.6 μM and 0.12 μM, respectively. A rapid response time of 4 min was found for the detection of Hg²⁺ by the nano-probe. The effect of pH and temperature on the detection of Hg²⁺ was also investigated. The nano-probe was successfully applied for the detection of Hg²⁺ from tap and river water.