Surface Modification of Magnetite with Carboxyl Arylated Gold Nanoparticles for Capture and Removal of Bacteria

This study presents a novel synthesis method for fabricating magnetic-plasmonic Fe₃O₄@CS-AuNPs nanocomposite utilizing aryldiazonium gold(III) salts. The low reduction potential of aryldiazonium gold salts enables their spontaneous reduction on the surface of Fe₃O₄ NPs stabilized with chitosan (CS), as CS facilitates the electron transfer process. The Fe₃O₄@CS-AuNPs nanocomposite exhibited gold plasmon peaks at 525 nm in UV-vis spectra and demonstrated long shelf life in an aqueous solution, with a ζ-potential of -42.8 mV. XPS revealed the complete reduction of gold(III) supported by the Au 4f peak for Fe₃O₄@CS-AuNPs. The increased Fe(II) ratio in XPS suggests a green reduction, where chitosan reduced Au(III) to Au(0). HR-TEM images demonstrated that Fe₃O₄@CS-AuNPs have an average nanoparticle size of 17.0 ± 3.8 nm. The high surface area of 55.15 m²/g for Fe₃O₄@CS-AuNPs supports their enhanced adsorption and removal of E. coli bacteria. Fe₃O₄@CS-AuNPs exhibited superior removal efficiencies of 100%, 99%, and 97%, outperforming Fe₃O₄@CS bacteria removal of 3%, 21%, and 40%. Surface modification with arylated AuNPs enhanced the adsorption and bacterial binding, enabling Fe₃O₄@CS-AuNPs to demonstrate high capture efficiency and bactericidal activity, eliminating viable bacteria at a minimum inhibitory concentration (MIC) of 50%. These findings highlight the potential of Fe₃O₄@CS-AuNPs for enhanced microbial removal.