Antibacterial metal nanoclusters

Abstract

Combating bacterial infections is one of the most important applications of nanomedicine. In the past two decades, significant efforts have been committed to tune physicochemical properties of nanomaterials for the development of various novel nanoantibiotics. Among which, metal nanoclusters (NCs) with well-defined ultrasmall size and adjustable surface chemistry are emerging as the next-generation high performance nanoantibiotics. Metal NCs can penetrate bacterial cell envelope more easily than conventional nanomaterials due to their ultrasmall size. Meanwhile, the abundant active sites of the metal NCs help to catalyze the bacterial intracellular biochemical processes, resulting in enhanced antibacterial properties. In this review, we discuss the recent developments in metal NCs as a new generation of antimicrobial agents. Based on a brief introduction to the characteristics of metal NCs, we highlight the general working mechanisms by which metal NCs combating the bacterial infections. We also emphasize central roles of core size, element composition, oxidation state, and surface chemistry of metal NCs in their antimicrobial efficacy. Finally, we present a perspective on the remaining challenges and future developments of metal NCs for antibacterial therapeutics. Graphical Abstract

Ultrasmall Metal Nanoclusters: Multifunctional Materials Used in Medical Research

“…The antimicrobial mechanisms of ultrasmall metal NCs can be divided according to the following aspects (Figure 6): cell wall and cell membrane disruption, metal ion release, toxic reactive oxygen species (ROS) production, intracellular component disturbance, antimicrobial agent delivery, and photoactivation mechanisms. [19] Wang et al synthesized high-purity Au25 NCs and found that their killing effect on Gram-negative bacteria (Escherichia coli) was significantly better than that against Gram-positive bacteria (Staphylococcus aureus [S. aureus]) (Figure 7) at certain concentrations and after treatment for different lengths of time. After further investigation of their antibacterial mechanism, it was determined that bacterial cell death was mainly due to the synergistic effects of membrane and DNA damage, oxidative stress, and energy metabolism alterations, showing the potential of these NCs as a nanoantibiotic.…”

“…[60] In addition to Au NCs, Ag NCs, Cu NCs, alloy NCs, and related composite nanostructures also have antimicrobial applications, which are related to their basic composition and individual properties. [19] Zheng et al established a library of full-spectrum water-soluble AuxAg25MHAx(-)18NCs. When the alloy composition was extended to the full spectral range, showing U-shaped antimicrobial behavior, the alloy nanomaterials usually exhibited better performance in applications, indicating that alloy nanomaterials have unexpected complexity and deserve further investigation by multidisciplinary groups.…”

“…The antimicrobial mechanisms of ultrasmall metal NCs can be divided according to the following aspects ( Figure ): cell wall and cell membrane disruption, metal ion release, toxic reactive oxygen species (ROS) production, intracellular component disturbance, antimicrobial agent delivery, and photoactivation mechanisms. [ 19 ]…”

“…[ 60 ] In addition to Au NCs, Ag NCs, Cu NCs, alloy NCs, and related composite nanostructures also have antimicrobial applications, which are related to their basic composition and individual properties. [ 19 ] Zheng et al. established a library of full‐spectrum water‐soluble AuxAg25MHAx(‐)18NCs.…”

“…[ 18 ] Moreover, the ultrasmall size of metal NCs allows them to penetrate bacterial cell membranes more easily, and their unique physicochemical properties such as optical, electromagnetic, and catalytic properties as well as their inherent advantages in structure make them of increasing interest for antimicrobial applications. [ 19 ] Existing studies have shown that the unique fluorescence properties of metal NCs, ultrasmall size, good photostability, low cytotoxicity, and good biocompatibility conditions make them also important in bioimaging. [ 20 ] In addition, it has been documented that metal NCs are involved in anti‐inflammation and the promotion of wound healing.…”