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 FeO@CS-AuNPs nanocomposite utilizing aryldiazonium gold(III) salts. The low reduction potential of aryldiazonium gold salts enables their spontaneous reduction on the surface of FeO NPs stabilized with chitosan (CS), as CS facilitates the electron transfer process. The FeO@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 FeO@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 FeO@CS-AuNPs have an average nanoparticle size of 17.0 ± 3.8 nm. The high surface area of 55.15 m/g for FeO@CS-AuNPs supports their enhanced adsorption and removal of bacteria. FeO@CS-AuNPs exhibited superior removal efficiencies of 100%, 99%, and 97%, outperforming FeO@CS bacteria removal of 3%, 21%, and 40%. Surface modification with arylated AuNPs enhanced the adsorption and bacterial binding, enabling FeO@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 FeO@CS-AuNPs for enhanced microbial removal.