Metal nanoclusters (NCs) with unique chemical and physical properties have been extensively demonstrated to be emerging nanoantibiotics for fighting bacterial infections. Understanding the antibacterial mechanisms of metal nanoclusters is important for evaluating their clinical applications as nanoantibiotics. To understand the antibacterial mechanism, gold nanoclusters (AuNCs) were applied as an antibacterial agent for real-time observations of their interactions with bacteria by in situ transmission electron microscopy (TEM). In this work, a surface ligand of glutathione-conjugated (GSH)-AuNCs was prepared via a simple hydrothermal method. Optical and structural characterizations validated the successful preparation of GSH-AuNCs. Bacterial growth curves of Acetobacter aceti revealed that the antibacterial activity of GSH-AuNCs increased with the weight concentration. The antibacterial activity of GSH-AuNCs was confirmed by the intracellular reactive oxygen species (ROS) generation induced by GSH-AuNCs in A. aceti. Furthermore, real-time observations of interactions between GSH-AuNCs and A. aceti were made using in situ liquid cell TEM. Based on the results of real-time observations, GSH-AuNCs first attached onto the bacterial membranes of A. aceti by physical adsorption and then penetrated into A. aceti by internalization. Eventually, the production of intracellular ROS induced by GSH-AuNCs caused destruction of the bacterial membranes, which led to the death of A. aceti. After the bacterial membranes had been destroyed, A. aceti eventually died.

Background: Metal nanoclusters (NCs) with outstanding structural and optical properties have been intensively validated for applications in nanomedicine and nanotechnology. Carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6) is overexpressed in many cancer cells. Objective: The gold nanoclusters conjugated with a single domain antibody targeting CEACAM6 of 2A3 (2A3-AuNCs) were synthesized for the inhibition of cancer cells. Methods: 2A3-AuNCs were prepared via a facile hydrothermal approach. The cell viability was measured by resazurin dye reduction assay. The cell death was analyzed by fluorescence imaging. Results: Structural and optical characterizations demonstrated the successful synthesis of 2A3-AuNCs with a roughly spherical shape and a size of 2.35 nm. The 2A3-AuNCs revealed a maximum fluorescence intensity at 350 nm with a fluorescence quantum yield of 4.0%. The cell viability assay indicated that 2A3-AuNCs could inhibit the growths of cancer cells with overexpressed CEACAM6, including breast cancer MDA-MB-231 and MDA-MB-468 cells. The fluorescence imaging results also demonstrated that 2A3-AuNCs could inhibit the growth of cancer cells with MDA-MB-231 and MDA-MB-468 cells. Conclusion: Combination with the results of cell viability assay and fluorescence imaging, the surface ligand of 2A3 antibody on 2A3-AuNCs exhibited promising inhibition of CEACAM6 overexpressed cancer cells. Our work provides a potential application of AuNCs in cancer therapy.

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