Bioactive Gold Nanoparticles Synthesized by Lactobacillus acidophilus for Catalytic and Antibacterial Applications

The biological synthesis of nanoparticles can potentially widen the possibilities for their applications by avoiding the involvement of hazardous chemicals. In this study, we used Lactobacillus acidophilus in an environmentally friendly way to produce gold nanoparticles (AuNPs) via extracellular means, which were confirmed by various physicochemical techniques. The surface-bound proteins and major carbon functional groups (C–H, C–C, and C–N) formed and stabilized the AuNPs. These AuNPs exhibited strong catalytic activity by reducing various dyes, including methylene blue, Congo red, methyl orange, and malachite green. Methylene blue and Congo red were reduced within 5 min, while methyl orange was reduced within 10 min, and malachite green showed a complete reduction reaction in 3 min in the presence of AuNPs with respective catalytic performance of 64.4, 5, 49.4, and 26.8% in the first cycle. These AuNPs were proven to be a moderate antioxidant agent by oxidizing 1, 1-diphenyl-2-picrylhydrazyl compound within 40 min. A thin layer of AuNPs on the disposable carbon electrode showed their electrochemical sensitivity, which can provide an excellent platform for gold nanoparticle-based biosensors. The bactericidal effect of these AuNPs was tested against Escherichia coli and Listeria monocytogenes, and their antibacterial properties were exposed by compromising cellular integrity, shown as damaged membranes and demolished cells. The distinguishable antibacterial effect of AuNPs was detected using metamaterial-based terahertz spectroscopy in our study, demonstrating its potential for rapid, noninvasive detection of microbial contamination on eggshells and crab shells, ensuring improved food safety and quality control. The synthesis approach used in this study is environmentally friendly and can produce biochemically active metal nanoparticles without involving environmental hazards.