Colorimetric-based detection of enteric bacterial pathogens using chromogens-functionalized iron oxide-gold nanocomposites biosynthesized by Bacillus subtilis

Abstract

Bio-functionalized nanomaterial has emerged as a promising technique for colorimetric detection of foodborne pathogens to promote food safety and quality. For this study, we evaluated the performance of novel chromogen-functionalized iron oxide-gold nanocomposites (Fe3O4-AuNCs) for colorimetric detection of enteric bacteria. Iron oxide nanoparticles (Fe3O4-NPs) and gold nanoparticles (AuNPs) biosynthesized by Bacillus subtilis (B. 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). Fe3O4-AuNCs were formed using ethylenediaminetetraacetic acid-capped Fe3O4-NPs and polyethyleneimine (PEI)/polyethylene glycol (PEG)-immobilized AuNPs. Different functionalized-Fe3O4-AuNCs were derived from chromogens such as 2-Nitrophenyl-alpha-D-glucopyranoside (2-NPGP), urea, and 2,3,5,-triphenyl tetrazolium chloride (TTC). The performances of the developed chromogens-functionalized Fe3O4-AuNCs were evaluated on Staphylococcus aureus (S. aureus), Escherichia coli (E. coli), and Salmonella typhimurium (S. typhi). Biosynthesized Fe3O4-NPs and AuNPs revealed 261 and 548 nm absorbance spectra with mean sizes of 72 and 118 nm, respectively. The EDX spectra revealed an increased percentage of elemental gold in Fe3O4-AuNCs linked by PEI than in Fe3O4-AuNCs linked by PEG (75.56%;61.40%). However, a reduced percentage of iron was observed in Fe3O4-AuNCs linked by PEI than in Fe3O4-AuNCs linked by PEG (7.40%;20.00%). The 2-NPGP-functionalized Fe3O4-AuNCs linked by PEI showed a light pale colour with S. aureus and a limit of detection (LOD) of 104 CFU/mL. Urea-functionalized Fe3O4-AuNCs linked by PEI/PEG had no colour change with the test pathogens. TTC-functionalized Fe3O4-AuNCs linked by PEI revealed an intense red colour with S. typhi and E. coli within 2 and 6 h, respectively, and a 108 CFU/mL LOD. This study showed that TTC-functionalized Fe3O4-AuNC linked by PEI is promising for detecting S. typhi and E. coli.