Shell thickness-dependent antibacterial activity and biocompatibility of gold@silver core–shell nanoparticles

Authors: YANG, LONGPING - Nanjing Agricultural University; YAN, WENJING - Nanjing Agricultural University; WANG, HONGXIA - Nanjing Agricultural University; Zhuang, Hong; ZHANG, JIANHAO - Nanjing Agricultural University

Submitted to: RSC Advances
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2017
Publication Date: 2/14/2017
Citation: Yang, L., Yan, W., Wang, H., Zhuang, H., Zhang, J. 2017. Shell thickness-dependent antibacterial activity and biocompatibility of gold@silver core–shell nanoparticles. RSC Advances. 7:11355-11361.

Interpretive Summary: Microbiological safety and spoilage have been challenges to the modern society and are increasing concerns to consumers. Many antimicrobial treatments have been developed, applied, and/or evaluated for control of the microbiological safety and spoilage. Nano-sized materials are a new type of antimicrobial materials for improvement of microbiological safety and control of microbiological spoilage. Among different antimicrobial nanomaterials, silver nanoparticles (Ag NPs) are the most promising agent because of their high thermal stability, limited microbial resistance, and broad-spectrum antimicrobial activity. But, the easy oxidation of pure Ag NPs and their toxicity to human cells have limited Ag NP applications. In the present study, Au@Ag NPs with different shell thickness were fabricated and their antibacterial activities were investigated against both Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus) and the cytotoxicity toward SH-SY5Y human cells. Our results demonstrate that the Au@Ag NPs with a thickness of 5 nm or Au:Ag ratio 1:1 (Au@Ag-2 NPs) have the highest antibacterial activity with little damage to the human cells. The minimum inhibitory concentrations of Au@Ag- NPs are significant lower than that of Ag NPs or the simple mixture of Ag and Au NPs, suggesting the synergistic effects of Au and Ag in core–shell NPs. These data indicate that Au@Ag NPs may be effective antibacterial agents for pathogen control in hospitals and food processing.

Technical Abstract: Antimicrobial activity of silver is highly effective and broad-spectrum; however, poor long-term antibacterial efficiency and cytotoxicity toward mammalian cells have restricted their applications. Here, we fabricated Au@Ag NPs with tailored shell thickness, and investigated their antibacterial activities against both Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus) and the cytotoxicity toward SH-SY5Y human cells, for the first time. Our results demonstrate that Au@Ag NPs with a thickness of 5 nm or Au : Ag ratio 1 : 1 (Au@Ag-2 NPs) have the highest antibacterial activity and excellent biocompatibility. The minimum inhibitory concentration (MIC) values of Au@Ag-2 NPs in terms of effective silver concentration are 5 µg/mL for E. coli and 7.5 µg/mL for S. aureus, which is significant lower than that of Ag NPs or the simple mixture of Ag and Au NPs and suggests the synergistic effects of Au and Ag in core–shell NPs. Live/dead bacterial assay and scanning electron microscope (SEM) images demonstrated that the Au@Ag NPs disrupt the bacterial cell membrane which subsequently results in cellular material leakage and cell death. The Au@Ag NPs may have great potential as effective antibacterial agents for pathogen control in hospitals and food processing.