6-Mercaptohexanoic Acid-Conjugated Gold Nanoclusters (AuNCs-MHA) as an Antibacterial Agent Against Gram-negative and Gram-positive Bacteria

In several regions of the world, bacterial antibiotic resistance is a major concern. Nanotechnology is one of the options created to address these issues. The selection of surface ligands will affect the stability, solubility, and physical and chemical properties of ultrasmall gold nanoclusters (AuNCs). Ultrasmall gold nanoclusters (AuNCs) are nanomaterials comprised of noble metals with unique features. AuNCs could serve as antibacterial agents. To understanding how AuNCs can be used in therapeutic applications, it is necessary to comprehend the killing mechanism and effectiveness of bacteria. Here, we present AuNCs produced with the ligand 6-mercaptohexanoic acid and the antibacterial mechanism found in Gram-negative (E. coli) and Gram-positive bacteria (S. aureus). We discovered that AuNCs-MHA were effectively disseminated and had a uniform size distribution, with a size of approximately 1-2 nm. The surface charge of AuNCs-MHA was negative, with a zeta potential of -22.8 ± 5.18 mV. Regarding its antibacterial efficacy, when exposed to a concentration of 4 mg/mL, AuNCs-MHA has demonstrated a notable eradication rate of 90% for E. coli, whereas it achieved an 80% elimination rate for S. aureus. These findings align with the observed generation of reactive oxygen species (ROS), where E. coli exhibited a 4-fold increase compared to S. aureus, which displayed a 2.5-fold rise. This outcome implies that Gram-negative bacteria display greater susceptibility to the antibacterial effects of AuNCs-MHA in comparison to Gram-positive bacteria. This study is expected to contribute to the assessment of the nanocluster's potential as a nanoantibiotic in the treatment of bacterial infections. Furthermore, AuNCs offer a promising platform for investigating antimicrobial mechanisms, especially in the context of multidrug-resistant (MDR) bacteria, thereby enhancing their appeal for various medical applications.