Does the Antibacterial Activity of Silver Nanoparticles Depend on the Shape of the Nanoparticle? A Study of the Gram-Negative Bacterium Escherichia coli

Abstract

In this work we investigated the antibacterial properties of differently shaped silver nanoparticles against the gram-negative bacterium Escherichia coli, both in liquid systems and on agar plates. Energy-filtering transmission electron microscopy images revealed considerable changes in the cell membranes upon treatment, resulting in cell death. Truncated triangular silver nanoplates with a {111} lattice plane as the basal plane displayed the strongest biocidal action, compared with spherical and rod-shaped nanoparticles and with Ag ؉ (in the form of AgNO 3 ). It is proposed that nanoscale size and the presence of a {111} plane combine to promote this biocidal property. To our knowledge, this is the first comparative study on the bactericidal properties of silver nanoparticles of different shapes, and our results demonstrate that silver nanoparticles undergo a shape-dependent interaction with the gram-negative organism E. coli.Over the past few decades, inorganic nanoparticles, whose structures exhibit significantly novel and improved physical, chemical, and biological properties, phenomena, and functionality due to their nanoscale size, have elicited much interest. Nanophasic and nanostructured materials are attracting a great deal of attention because of their potential for achieving specific processes and selectivity, especially in biological and pharmaceutical applications (5, 39).Discoveries in the past decade have demonstrated that the electromagnetic, optical, and catalytic properties of noble-metal nanocrystals are strongly influenced by shape and size (6,26). This has motivated an upsurge in research on the synthesis routes that allow better control of shape and size (18,34,41), with projected applications in nanoelectronics and spectroscopy (14,19,36).Recent studies have demonstrated that specially formulated metal oxide nanoparticles have good antibacterial activity (33), and antimicrobial formulations comprising nanoparticles could be effective bactericidal materials (11,12).Among inorganic antibacterial agents, silver has been employed most extensively since ancient times to fight infections and control spoilage. The antibacterial and antiviral actions of silver, silver ion, and silver compounds have been thoroughly investigated (28,29,37). However, in minute concentrations, silver is nontoxic to human cells. The epidemiological history of silver has established its nontoxicity in normal use. Catalytic oxidation by metallic silver and reaction with dissolved monovalent silver ion probably contribute to its bactericidal effect (17). Microbes are unlikely to develop resistance against silver, as they do against conventional and narrow-target antibiotics, because the metal attacks a broad range of targets in the organisms, which means that they would have to develop a host of mutations simultaneously to protect themselves. Thus, silver ions have been used as an antibacterial component in dental resin composites (15), in synthetic zeolites (22), and in coatings of medical devices (2).Recent literature r...

Strain specificity in antimicrobial activity of silver and copper nanoparticles

“…As concentration of nanoparticles increased to MIC of the respective strains, no growth was observed in the flask. The bactericidal effect of nanoparticles is dependent on the concentration of nanoparticles and the initial bacterial concentration [24]. In this study, the initial bacterial concentration was almost constant at 10 3 -10 4 CFU ml À1 irrespective of nanoparticle concentration and microbial strain.…”

“…Some of the silver nanoparticles also penetrate into the cells. It is reported that the bactericidal effect of silver nanoparticles decreases as the size increases and is also affected by the shape of the particles [23,24]. Although most studies have utilized spherical particles, truncated triangular shaped particles are reported to have greater bactericidal effect compared to that of spherical and rodshaped particles [24].…”

Antibacterial activity of silver nanoparticles: A surface science insight

“…Finally, the requirement of the Ag NPs to dissolve and to release Ag + ions can contribute explaining the size and shape dependency of the nanoparticle action [62]. Most studies show indeed a size dependency of the antimicrobial activity of (quasi-spherical) nanoparticles, the smaller being the more active [63].…”

Catharanthus roseus: a natural source for the synthesis of silver nanoparticles

“…Nanoparticles present a higher surface area to volume ratio with decrease in the size of the particles. Specific surface area is relevant to catalytic activity and other related properties such as antimicrobial activity of AgNPs [3][4][5] . As the specific surface area of nanoparticles is increased, their biological effectiveness can also increase on the account of a rise in surface energy.…”