Fluorometric Zn2+ detection with gallic acid passivated Fe-Ag bimetallic nanocomposites

Tuning of metal-enhanced fluorescence (MEF) involving silver nanoparticle surface and weak fluorophore for nano-sensing is an active area of research. Gallic acid-capped iron nanoparticles could generate strong MEF by introducing Ag⁺ in the reaction mixture, and Zn²⁺ quenched fluorescence exclusively. Thus, gallic acid-capped FeAg nanocomposite performed as an ideal sensing platform for the detection of Zn²⁺ (limit of detection 1 × 10⁻⁶ M, linear detection range 5 × 10⁻⁹ to 5× 10⁻⁶M). Improved scattering cross section at ideal distance (5–90 nm), lightning rod effect, and higher rate of emission are attributed to silver-enhanced fluorescence. On the contrary, Zn²⁺ induced quenching was associated with the formation of the lossy surface wave due to energy transfer from the metal surface and fluorophore towards ZnO, following the radiating plasmon model.