From Unimolecular Template to Silver Nanocrystal Clusters: An Effective Strategy to Balance Antibacterial Activity and Cytotoxicity

Abstract

Silver nanomaterials have attracted a great deal of interest due to their broad-spectrum antimicrobial activity. However, it is still challenging to balance the high antibacterial efficiency with low damage to biological cells of silver nanostructures, especially when the diameter decreases to less than 10 nm. Here, we developed a new type of Ag nanohybrid material via a unimolecular micelle template method, which presents amazing antibacterial activities and almost noncytotoxicity. First, watersoluble multiarm star-shaped brushlike copolymer α-CD-g-[(PEO 40 -g-PAA 50 )-b-PEO 5 ] 18 was precisely synthesized and its micelle behavior in different solvents was revealed. Then, nanocrystal clusters assembled by Ag grains (Ag@Template NCs) were prepared through an in situ redox route using the unimolecular micelle of α-CD-g-[(PEO 40 -g-PAA 50 )-b-PEO 5 ] 18 as the soft template, AgNO 3 as a precursor, and tetrabutylammonium borohydride (TBAB) as the reducing agent. The overall size of the achieved Ag@Template NCs is controlled by the template structure at around 40 nm (D h in DMF), and the size of the Ag grain can be easily regulated from ∼1 to ∼5 nm by adjusting the feeding ratio of AgNO 3 /acrylic acid (AA) units in the template from 1:10 to 1:1. Benefitting from the structural design of the template, all Ag@Template NCs prepared here exhibit excellent dispersibility and chemical stability in different aqueous environments (neutral, pH = 5.5, and 0.9% NaCl physiological saline solution), which play a crucial role in the long-term storage and potential application in a complex physiological environment. The antibacterial and cytotoxicity tests indicate that Ag@Template NCs display much better performance than Ag nanoparticles (Ag NPs), which have a comparable overall size of ∼25 nm. The inhibitory capability of Ag@Template NCs to bacteria strongly depends on the grain size. Specifically, the Ag@ Template-1 NC assembled by the smallest grains (1.6 ± 0.3 nm) presents the best antibacterial activity. For E. coli (−), the MIC value is as low as 5 μg/mL (0.36 μg/mL of Ag), while for S. aureus (+), the value is around 10 μg/mL (0.72 μg/mL of Ag). The survival rate of L02 cells and lactate dehydrogenase assay together illustrate the low cytotoxicity possessed by the prepared Ag@ Template NCs. Therefore, the proposed Ag@Template NC structure successfully resolves the high reactivity, instability, and fast oxidation issues of the ultrasmall Ag nanoparticles, and integrates high antibacterial efficiency and nontoxicity to biological cells into one platform, which implies its broad potential application in biomedicine.

Facile Synthesis of Carbon Dot Deposited γ-FeOOH Nanosheet/Polypyrrole Composite: A Robust Photocatalyst for Degradation of Antibiotics under Sunlight Irradiation with Enhanced Antibacterial Activity

“…Figure c,f shows the significant ZOI exhibited by standard antibiotic ciprofloxacin and represented as positive control, whereas no ZOI was observed in the case of the negative control, i.e., DI water (Figure S11), for both bacterial strains. The principal mechanism behind the antibacterial activity of PFL/CDs-2 composite may be ascribed to the formation of oxidative stress by reactive oxygen species (ROS) such as hydroxyl radicals ( • OH) and superoxide radicals ( • O 2 – ), which are adhered to the microbial cells and then damage the cell membrane. , The present work reports the synergic effect of γ-FeOOH, CDs, and PPy, which results in the generation of more ROS compared to individual components, which plays a major role in the inhibition of pathogenic bacteria. Moreover, the combined effects of γ-FeOOH, CDs, and PPy improve the antibacterial activity of the PFL/CDs-2 composite, where ferric oxyhydroxides (γ-FeOOH) can play an important role in surface inactivation of microbes due to the electrostatic attraction between positively charged ferric oxyhydroxides and negatively charged bacterial cells. , The antibacterial activity of the PPy arises due to the positive charge on the N atom of the PPy backbone .…”

Simultaneous in Situ Exfoliation of Titanate and Zn–Cr Layered Double Hydroxides with a Copolymer for Photocatalytic Degradation of Organic Pollutants

“…The high antimicrobial activity of g-Dext/LT/LDH could be ascribed to the possible combined roles of the material as follows: (a) the presence of remarkable antibacterial ions such as Zn 2+ , which diffused onto the LB agar media and prevented the bacterial growth over a specific area. The inhibition mechanism of Zn 2+ could be attributed to its positive charge, which can easily adhere to the negatively charged cell membrane of bacteria and provide opposite charge distribution of the cell membrane, thereby damaging the cell membrane; (b) the generation of ROS such as • OH and • O 2 – on the surface of titanate and LDH nanosheets may inhibit bacterial activity by oxidizing the lipid bilayer of the bacteria; , (c) the additional antibacterial activity of the pDMAEMA moiety, which has a high charge density, including the hydrophilic/hydrophobic balance in the polymer; (d) the increased surface area of the material, which gives superior contact with the bacteria cell wall …”

A silver-functionalized metal–organic framework with effective antibacterial activity

“…This value is among the best of the state-of-the-art Ag-based antibacterial materials (1.4, 3.8, 4.5, 6.3 μg Ag cm −3 ). 24–27 The effective antibacterial activity of Ag@Zn-MOF can be attributed to the homogenously dispersed Ag sites within the alkene-functionalized Zn-MOF, which maximizes the accessibility of Ag species and reduces the use of Ag.…”

“…Ag@Zn-MOF reaches ∼100% bacterial reduction at a concentration of 25 μg MOF cm −3 (corresponding to 1.7 μg Ag cm −3 ), which is among the best of the state-of-art Ag-based antibacterial agents (1.4–6.3 μg Ag cm −3 ). 24–27…”