Search

Antibacterial activity of zinc oxide nanoparticles (ZnO-NPs) has received significant interest worldwide particularly by the implementation of nanotechnology to synthesize particles in the nanometer region. Many microorganisms exist in the range from hundreds of nanometers to tens of micrometers. ZnO-NPs exhibit attractive antibacterial properties due to increased specific surface area as the reduced particle size leading to enhanced particle surface reactivity. ZnO is a bio-safe material that possesses photo-oxidizing and photocatalysis impacts on chemical and biological species. This review covered ZnO-NPs antibacterial activity including testing methods, impact of UV illumination, ZnO particle properties (size, concentration, morphology, and defects), particle surface modification, and minimum inhibitory concentration. Particular emphasize was given to bactericidal and bacteriostatic mechanisms with focus on generation of reactive oxygen species (ROS) including hydrogen peroxide (HO), OH (hydroxyl radicals), and O (peroxide). ROS has been a major factor for several mechanisms including cell wall damage due to ZnO-localized interaction, enhanced membrane permeability, internalization of NPs due to loss of proton motive force and uptake of toxic dissolved zinc ions. These have led to mitochondria weakness, intracellular outflow, and release in gene expression of oxidative stress which caused eventual cell growth inhibition and cell death. In some cases, enhanced antibacterial activity can be attributed to surface defects on ZnO abrasive surface texture. One functional application of the ZnO antibacterial bioactivity was discussed in food packaging industry where ZnO-NPs are used as an antibacterial agent toward foodborne diseases. Proper incorporation of ZnO-NPs into packaging materials can cause interaction with foodborne pathogens, thereby releasing NPs onto food surface where they come in contact with bad bacteria and cause the bacterial death and/or inhibition. [ABSTRACT FROM AUTHOR]

The structural morphology and in vitro toxicity of nano- and micro-sized ZnO structures were investigated. All the ZnO samples were characterized to determine their morphologies, particle sizes, structures and optical bandgaps. Transmission electron microscopy and field-emission scanning electron microscopy results revealed that the morphologies of nano-sized ZnO-N1 and ZnO-N2 samples consisted of spherical and irregularly-shaped particles, respectively. The corresponding particle sizes were 20–40 nm and 50–80 nm, respectively. The morphologies of micro-sized ZnO-M1 and ZnO-M2 samples were found to be mostly rod-structures and plate-structures, respectively. Rod diameters were 40–100 nm whereas plate widths were 50–150 nm. ZnO-N1 had the highest toxicity towards the cells, causing the cell viability to be less than 70% for all concentration ranges. This phenomenon was due to the small particle size and release of zinc ions. Micro-sized ZnO-M1 and ZnO-M2 samples had toxicity limits of 0.3 mM at most. [ABSTRACT FROM AUTHOR]

ZnO with two different morphologies were used to study the inhibition of Streptococcus sobrinus and Streptococcus mutans which are closely associated with tooth cavity. Rod-like shaped ZnO-A and plate-like shaped ZnO-B were produced using a zinc boiling furnace. The nanopowders were characterized using energy filtered transmission electron microscopy (EFTEM), X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, Raman spectroscopy and dynamic light scattering (DLS) to confirm the properties of the ZnO polycrystalline wurtzite structures. XRD results show that the calculated crystallite sizes of ZnO-A and ZnO-B were 36.6 and 39.4 nm, respectively, whereas DLS revealed particle size distributions of 21.82 nm (ZnO-A) and 52.21 nm (ZnO-B). PL spectra showed ion vacancy defects related to green and red luminescence for both ZnO particles. These defects evolved during the generation of reactive oxygen species which contributed to the antibacterial activity. Antibacterial activity was investigated using microdilution technique towards S. sobrinus and S. mutans at different nanopowder concentrations. Results showed that ZnO-A exhibited higher inhibition on both bacteria compared with ZnO-B. Moreover, S. mutans was more sensitive compared with S. sobrinus because of its higher inhibition rate. [ABSTRACT FROM AUTHOR]

Abstract: The antibacterial responses of zinc oxide (ZnO) structures against Staphylococcus aureus, Pseudomonas aeruginosa, and Streptococcus pyogenes were investigated. Two ZnO powder samples, one with rod-like (ZnO-1) and the other with plate-like (ZnO-2) structures, were characterized for their morphological, structural, and optical properties. The rods were 30–120nm in diameter, and the plates were 40–100nm thick. XRD results revealed the wurtzite crystallinity of ZnO with average crystallite sizes of 33.72 (ZnO-1) and 39.25 (ZnO-2)nm. ZnO-2 possessed a relatively higher green photoluminescence than that of ZnO-1, suggesting a relatively higher amount of oxygen vacancies in ZnO-2 structures. Optical density measurements showed that both ZnO samples inhibited the growth of S. aureus, P. aeruginosa, and S. pyogenes by 29–98% after 24h of treatment. The most dramatic growth inhibition was observed in S. pyogenes with 96% and 98% inhibition for ZnO-1 and ZnO-2, respectively, leading to a probable bactericidal phenomenon. The toxicological effect on S. pyogenes was probably due to the absence of catalase, making the bacteria vulnerable to the harmful reactive oxygen species (ROS) released by ZnO. ZnO-1 induced higher inhibition toward S. aureus and P. aeruginosa than that of ZnO-2 because of the smaller particle size of rod structures compared to plate and slab structures. The adhesion of ZnO particles on the membrane of bacteria could be the underlying cause of zinc toxicity effect towards the bacteria. ZnO-1 possessed larger surface area and provided higher amount of zinc atom, thereby inducing higher level of toxicity toward the bacteria. Two possible mechanisms were proposed to explain the inhibition of bacteria, namely, ROS toxicity toward cellular constituents and interaction of zinc with bacteria membrane through adhesion of ZnO particle. Several ZnO morphological-antibacterial correlations were presented in this work. [Copyright &y& Elsevier]

Highlights: [•] UVA illumination on surface of ZnO pellet improves the surface conductance significantly. [•] Oxygen annealing halved the UV emission intensity and green emission intensity. [•] Oxygen annealing and UVA illumination increase the inhibition of E. coli and S. aureus growth. [•] Release of reactive oxygen species was proposed to cause bacteriostatic effect toward E. coli and S. aureus. [ABSTRACT FROM AUTHOR]