Antimicrobial Gold Nanoclusters: Recent Developments and Future Perspectives

Abstract

Bacterial infections have caused serious threats to public health due to the antimicrobial resistance in bacteria. Recently, gold nanoclusters (AuNCs) have been extensively investigated for biomedical applications because of their superior structural and optical properties. Great efforts have demonstrated that AuNCs conjugated with various surface ligands are promising antimicrobial agents owing to their high biocompatibility, polyvalent effect, easy modification and photothermal stability. In this review, we have highlighted the recent achievements for the utilizations of AuNCs as the antimicrobial agents. We have classified the antimicrobial AuNCs by their surface ligands including small molecules (< 900 Daltons) and macromolecules (> 900 Daltons). Moreover, the antimicrobial activities and mechanisms of AuNCs have been introduced into two main categories of small molecules and macromolecules, respectively. In accordance with the advancements of antimicrobial AuNCs, we further provided conclusions of current challenges and recommendations of future perspectives of antimicrobial AuNCs for fundamental researches and clinical applications.

Keywords: antimicrobial agent; antimicrobial mechanism; gold nanoclusters; macromolecule; small molecule.

Figure 1

Antimicrobial activity of MHA-AuNCs due to the increase of interaction between MHA-AuNCs and bacteria. Reproduced with permission from Reference [71]. Copyright © 2017, American Chemical Society.

Figure 2

Representative scheme of DPAu/AMD as a nanotheranostic agent. Reproduced with permission from Reference [72]. Copyright © 2014, American Chemical Society.

Figure 3

(A) Antibacterial effect of Man-AuNCs with their concentrations from 0 to 400 nM. (B) Colony formation of E. coli on LB agar plates in the (a) absence and (b) presence of Man-AuNCs (250 nM). Insets of Figure 3A indicate photographs of E. coli (1.0×10⁸ CFU/mL) grown for 10 h in the LB medium in the (a) absence and (b) presence of Man-AuNCs (250 nM). Reproduced with permission from Reference [74]. Copyright © 2011, Elsevier.

Figure 4

Antibacterial activities of AuNCs conjugated with different ligands by measuring their MICs. The lower MIC of AuNCs show higher antibacterial activity. Reproduced with permission from Reference [75]. Copyright © 2018, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Figure 5

The mechanisms of cell membrane destruction, DNA damage and ROS generation for AuDAMP to kill bacteria. Reproduced with permission from Reference [76]. Copyright © 2018, American Chemical Society.

Figure 6

Surface ligand chemistry of AuNCs could determine their antimicrobial ability. Reproduced with permission from Reference [77]. Copyright © 2018, American Chemical Society.

Figure 7

(A) Antimicrobial activities of AuNC-L-Amp and free-Amp at different incubation times for MRSA1 and 2. SEM images of MRSA incubation with (B) PBS, (C) AuNC-L, (D) Free-Amp and (E) AuNC-L-Amp. SEM images indicate that AuNC-L and free-Amp did not cause the changes of bacterial morphology. On the other hand, AuNC-L-Amp induced the cellular structure of MRSA. Reproduced with permission from Reference [79]. Copyright © 2018, Springer Nature.

Figure 8

(a) Antibacterial activity of Au-SGaa-Van, vancomycin and Au-SGaa against Gram-positive S. aureus. (b) Antibacterial activity of Au-SGaa-Van, vancomycin and Au-SGaa against Gram-negative E. coli. Reproduced with permission from Reference [81]. Copyright © 2018, Royal Society of Chemistry.

Figure 9

Illustration of interaction between SAuNCs, lipid A of LPS and sepsis progression. Reproduced with permission from Reference [82]. Copyright © 2018, American Chemical Society.

Figure 10

(A) Illustration of preparations of AgNCs@Bacitracin, AuNCs@Bacitracin, and CuNCs@Bacitracin. (B) Bacteria incubated with AgNCs@Bacitracin, AuNCs@Bacitracin, or CuNCs@Bacitracin. Reproduced with permission from Reference [83]. Copyright © 2019, American Chemical Society.