Multifunctional Schiff base capped gold nanoparticles for optical recognition of silver ions with analytical applications and biological evaluation

In this study, a Schiff base 2,2’-((1E,1’E)-((1,2-diphenylethane-1,2-diylidene)bis(hydrazine-2,1-diylidene))bis(methaneylylidene))bis(4-nitrophenol) (DPHNP) has been employed as a capping reagent for the synthesis of gold nanoparticles in order to construct a dual-mode optical sensing system. The synthesized DPHNP@AuNPs (L) were thoroughly characterized by spectroscopic, microscopic and computational methods. The probe DPHNP@AuNPs (L) showed strong colorimetric and fluorescent responses upon the coordination-induced change of electronic transitions and plasmonic properties upon exposure to Ag + ions. The detection limit of the fluorometric test was 2.60 × 10 − 6 M and the binding constant was 1.0 × 10 4 M⁻¹, while that of the colorimetric test was 1.56 × 10 − 6 M and the binding constant was 2.7 × 10 6 M − 1 . The proposed sensor showed high recoveries for the determination of Ag + in various food and water samples and exhibited good selectivity, reversibility, and tolerance to interfering ions. Moreover, the nanocomposite DPHNP@AuNPs exhibited antioxidant and antibacterial properties, suggesting its potential as a versatile platform for environmental monitoring and other analytical applications.