Abstract
The spread of infectious diseases caused by microorganisms has been an emerging global issue. This is exacerbated by the antimicrobial resistance (AMR) of fungi, viruses, bacteria, and parasites to medicines. Nanotechnology, particularly the use of gold nanoparticles (AuNPs), is being explored to reduce antimicrobial-resistant strains. However, concerns about their toxicity and environmental impact are a major concern. This study aims to assess the antibacterial activity and toxicity of AuNPs synthesized by incorporating a heterocyclic compound 2-Imino-7-nitro-4-(4-chlorophenyl)-2H-1,3-thiazino[3,2-A] benzimidazole (FDM31) and with a Cola Lateritia stem bark extract (CLS). The optical characteristics, size and zeta potential, functional groups, elemental composition, crystalline structure, and morphology of the synthesized AuNPs were determined by ultraviolet-visible spectroscopy (UV-Vis), dynamic light scattering (DLS), Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscope-energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD) and Transmission electron microscopy (TEM), respectively. The antibacterial activity of synthesized AuNPs against three gram positive and negative bacterial strains and assessed their toxicity using the zebrafish embryo toxicity test (ZFET). UV-Vis and SEM-EDS confirmed the fabrication of the AuNPs. The average size and zeta potential of the AuNPs ranged between 17 to 30 nm and -13 to -33 mV, respectively. The AuNPs exhibited a cubic crystalline structure, as confirmed by XRD, while TEM analysis revealed spherical NPs with varying sizes. Green synthesis produced the highest Au weight at 33% compared to 15% with FDM31 synthesized NPs. The study found Mycobacterium smegmutis to be the most resistant to AuNP-FDM31 and AuNPs-CLS due to decreased response to exposure. AuNPs-FDM31 had the lowest MIC towards bacteria tested, making it the most effective. The green synthesis produced pure AuNPs, which were less toxic to zebrafish. These results suggest that capping the AuNPs reduces the risk of nanomaterials targeted at biomedical applications by modifying the surface chemistry, making them more effective and less toxic.
Keywords: Green synthesis, gold nanoparticles, heterocyclic compounds, Cola Lateritia stem bark extract, antibacterial activity and toxicity.