Affinity Capture Using Ligand and Polymer-Functionalized Iron Oxide, Gold and Iron-Gold Nanocomposites to Target Enteric Bacteria

In this study, the affinity potentials of biosynthesized and functionalized iron oxide nanoparticles (IONPs), gold nanoparticles (AuNPs), and iron-gold nanocomposites (Fe3O4-AuNCs) harnessed to target enteric pathogens were evaluated. Colloidal IONPs and AuNPs biosynthesized by Bacillus subtilis were monitored and characterized with UV-Vis spectroscopy, Fourier transform infrared (FTIR), scanning electron microscope (SEM), energy dispersive X-ray (EDX), and X-ray diffractometer (XRD). The synthesized nanoparticles were functionalized independently and as nanocomposites with the ligand (ethylenediaminetetraacetic acid (EDTA)) and polymers (polyethyleneimine (PEI) and polyethylene glycol (PEG)). Affinity capture of the derived functionalized nanoparticles and nanocomposites was evaluated on enteric bacteria and monitored at 540-600 nm wavelengths. Colloidal suspensions of the biosynthesized IONPs and AuNPs showed UV-Vis absorption peaks at 261 and 548 nm and mean distribution sizes of 72 and 83 nm, respectively. The energy dispersive X-ray (EDX) analysis showed 48.59% zerovalent iron oxide and 51.26% zerovalent gold. X-ray diffractometer (XRD) reported Bragg's peaks corresponding with the crystal lattice of iron oxide and gold nanoparticles. Capped Fe3O4-AuNCs functionalized with PEI had a significantly higher ratio of zerovalent gold (75.56%) compared to capped Fe3O4-AuNCs functionalized with PEG (61.40%); however, an increased zerovalent iron oxide (20.00%) than PEI-functionalized Fe3O4-AuNCs (7.40%). Capped Fe3O4-AuNCs showed significant binding affinities with Bacillus cereus, Salmonella typhi, Staphylococcus aureus, and Klebsiella aerogenes. The results show that ligands and polymers could enhance Fe3O4-AuNCs' ability to interact and bind to enteric bacterial pathogen's negatively charged cell wall (teichoic acid) and outer membrane (lipopolysaccharides). Biosynthesized and functionalized IONPs, AuNPs, and Fe3O4-AuNCs provide cost-effective and feasible nano-based detection of enteric bacteria.