Silver(I)-selective impedimetric and potentiometric detection at 3-hydroxy-N-(4-mercaptophenyl)benzamide functionalized gold surface – Analysis of water and packaged food products

Highlights: • HMB was synthesized via amide coupling. • Au-HMB self-assembly was characterized using CV, EIS, FTIR and AFM. • Au-HMB-Ag⁺ EIS sensor shows detection limit of 3.60 × 10⁻⁹ M. • AuNP-HMB-CPE sensor shows LOD of 4.46 × 10⁻⁵ M and Nernstian slope of 61.70 ± 0.02 mV/dec. • Sensors were successfully applied for analysis of water and packaged food samples. In the current work, a monothiol, 3-hydroxy-N-(4-mercaptophenyl) benzamide (HMB) was synthesized via amide coupling of 4-aminothiophenol with 3-hydroxybenzoic acid followed by its self-assembly on the surface of a gold electrode which was confirmed using electrochemical techniques: cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) and spectroscopic techniques: AFM and FT-IR. Further, HMB functionalized gold electrode (HMB-Au) was utilised as a platform for impedimetric sensing in the presence of one-electron reversible redox probe, [Fe(CN)₆]^3-/4- and found to show sensitivity towards Ag⁺ over a wide linear concentration range from 1 × 10⁻⁹ M to 1 × 10⁻⁴ M (r² = 0.99 ± 0.005) at pH = 8 with a detection limit of 3.60 × 10⁻⁹ M. Furthermore, HMB self-assembled Au nanoparticles (HMB-AuNPs) were incorporated as modifier to construct a carbon paste electrode (CPE) for potentiometric detection of Ag⁺. Ag⁺-CPE exhibited a Nernstian slope of 61.70 ± 0.02 mV per decade in the concentration range of 1.0 × 10⁻⁴ M - 1.0 × 10⁻¹ M (r² = 0.99 ± 0.01) with a detection limit of 4.46 × 10⁻⁵ M and a short response time of 15 s. Both HMB based EIS sensor and CPE have shown an acceptable selectivity towards silver(I) ions and successfully applied for estimation of silver(I) content in various samples of water and packaged food products.