Antibacterial properties and toxicity from metallic nanomaterials

Abstract

The era of antibiotic resistance is a cause of increasing concern as bacteria continue to develop adaptive countermeasures against current antibiotics at an alarming rate. In recent years, studies have reported nanoparticles as a promising alternative to antibacterial reagents because of their exhibited antibacterial activity in several biomedical applications, including drug and gene delivery, tissue engineering, and imaging. Moreover, nanomaterial research has led to reports of a possible relationship between the morphological characteristics of a nanomaterial and the magnitude of its delivered toxicity. However, conventional synthesis of nanoparticles requires harsh chemicals and costly energy consumption. Additionally, the exact relationship between toxicity and morphology of nanomaterials has not been well established. Here, we review the recent advancements in synthesis techniques for silver, gold, copper, titanium, zinc oxide, and magnesium oxide nanomaterials and composites, with a focus on the toxicity exhibited by nanomaterials of multidimensions. This article highlights the benefits of selecting each material or metal-based composite for certain applications while also addressing possible setbacks and the toxic effects of the nanomaterials on the environment.

Keywords: antibacterial reagents; antibiotic resistance; drug delivery; metals; nanomaterials; nanoscale; nanostructure; synthesis; toxicity.

Figure 1

Formation of reactive oxygen species (ROS) and disruption to membrane functionality by nanosilver. Notes: Antibacterial activities from silver are due to the formation of ROS and disruption of membrane functionality. Formation of ROS causes oxidative stress, which leads to cellular damage. The interaction between the released ions of nanosized silver results in disruption of the membrane functionality.

Figure 2

Damaged DNA strands due to silver ions in cell nucleus. Note: Nanosized silver releases silver ions, which interacts with DNA strands within the cellular nucleus, which results in DNA damage.

Figure 3

Nanosized gold exhibits antibacterial properties from prevention of ATPase and tRNA binding. Notes: The antibacterial activities of AuNPs are believed to proceed mainly in the two following ways: (A) a change in the membrane potential and a prevention of ATPase activities leading to a decline in cellular metabolism and (B) the subunit of the ribosome for tRNA binding is inhibited leading to a collapse in biological processes.

Figure 4

Copper oxide dimensions. Notes: Different copper oxide dimensions produce different amounts of antibacterial properties due to their ratio of surface area to volume. The simplest structure is a particle, then tube, followed by the sheet.

Figure 5

Comparison of released toxicity from microsized vs nanosized copper oxide. Notes: Due to the differences in the ratio of surface area to volume, toxicity levels are dependent on the size of copper oxide. Smaller structures such as (B) nanosized copper oxide compared to (A) microsized produce larger amounts of copper ions. The amount of toxicity is dependent on a number of copper ions released.

Figure 6

Titanium dioxide crystal structures. Notes: The three crystal structures of titanium dioxide show different amounts of antibacterial properties due to its production of •OH in its photocatalytic reaction, which causes cellular damage. (A) Anatase compared to other crystal structures such as (B) Brukide and (C) Rutile shows the most antibacterial activity.

Figure 7

Antibacterial activities due to titanium dioxide illumination. Nanotitanium dioxide produces antibacterial properties when (A) light illumination is present due to released hydroxyl radicals which cause cellular damage. (B) Without illumination of any kind, no antibacterial properties are produced.