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 (H2O2), OH− (hydroxyl radicals), and O2 −2 (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.

/pdf/review-on-zinc-oxide-nanoparticles-antibacterial-activity-2smaigi8sc.pdf

Review on Zinc Oxide Nanoparticles: Antibacterial Activity and Toxicity Mechanism.

The recent advances in nanotechnology and the corresponding increase in the use of nanomaterials in products in every sector of society have resulted in uncertainties regarding environmental impacts. The objectives of this review are to introduce the key aspects pertaining to nanomaterials in the environment and to discuss what is known concerning their fate, behavior, disposition, and toxicity, with a particular focus on those that make up manufactured nanomaterials. This review critiques existing nanomaterial research in freshwater, marine, and soil environments. It illustrates the paucity of existing research and demonstrates the need for additional research. Environmental scientists are encouraged to base this research on existing studies on colloidal behavior and toxicology. The need for standard reference and testing materials as well as methodology for suspension preparation and testing is also discussed.

Nanomaterials in the environment: Behavior, fate, bioavailability, and effects

The major strategies for designing surfaces that prevent fouling due to proteins, bacteria, and marine organisms are reviewed. Biofouling is of great concern in numerous applications ranging from biosensors to biomedical implants and devices, and from food packaging to industrial and marine equipment. The two major approaches to combat surface fouling are based on either preventing biofoulants from attaching or degrading them. One of the key strategies for imparting adhesion resistance involves the functionalization of surfaces with poly(ethylene glycol) (PEG) or oligo(ethylene glycol). Several alternatives to PEG-based coatings have also been designed over the past decade. While protein-resistant coatings may also resist bacterial attachment and subsequent biofilm formation, in order to overcome the fouling-mediated risk of bacterial infection it is highly desirable to design coatings that are bactericidal. Traditional techniques involve the design of coatings that release biocidal agents, including antibiotics, quaternary ammonium salts (QAS), and silver, into the surrounding aqueous environment. However, the emergence of antibiotic- and silver-resistant pathogenic strains has necessitated the development of alternative strategies. Therefore, other techniques based on the use of polycations, enzymes, nanomaterials, and photoactive agents are being investigated. With regard to marine antifouling coatings, restrictions on the use of biocide-releasing coatings have made the generation of nontoxic antifouling surfaces more important. While considerable progress has been made in the design of antifouling coatings, ongoing research in this area should result in the development of even better antifouling materials in the future.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201001215

Antifouling coatings: recent developments in the design of surfaces that prevent fouling by proteins, bacteria, and marine organisms.

Phytotoxicity of nanoparticles: Inhibition of seed germination and root growth

Comparative eco-toxicity of nanoscale TiO2, SiO2, and ZnO water suspensions.

In order to elucidate the antibacterial mechanisms of magnesium oxide (MgO), calcium oxide (CaO) and zinc oxide (ZnO), the generation of active oxygen from these ceramic powder slurries was examined by oxygen electrode analysis and chemiluminescence analysis. Hydrogen peroxide (H2O2) generated from the ZnO powder slurry was detected using the oxygen electrode. Active oxygen from the MgO and CaO powder slurries was not detected by the oxygen electrode analysis. Chemiluminescence analysis could detect the generation of active oxygen from three kinds of powders. The luminescence response of the CaO powder slurry was markedly strong. The chemiluminescence responses of the CaO and MgO powder slurries are due to the superoxide anion (O2–). The order of the strength of luminescence response was CaO, MgO, and ZnO, which agreed with that of the antibacterial activity of these powders. These results suggested that active oxygen species generated from the ceramic powders were associated with their antibacterial activities.

/pdf/detection-of-active-oxygen-generated-from-ceramic-powders-foq41r8u08.pdf

Detection of Active Oxygen Generated from Ceramic Powders Having Antibacterial Activity

The growth inhibitory effect of 26 ceramic powder slurries on bacteria was evaluated by measurement of the conductance change of the growth medium caused by bacterial metabolism (conductance method). Escherichia coli, Salmonella typhimurium, Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis were used as test bacteria. It was found that the growth of the test bacteria was inhibited by 10 ceramic powders. Magnesium oxide (MgO) and calcium oxide (CaO) powder slurries had a growth inhibitory effect on all test bacteria. In the cases of MgO, and CaO powder slurries, there was no difference in sensitivities among the test bacteria. These powder slurries exhibited bactericidal action on the test bacteria. On the other hand, the zinc oxide (ZnO) powder slurry inhibited the growth of Gram-positive bacteria stronger than Gram-negative bacteria. The effect was bacteriostatic action. The conductance method could provide quantitative and simple evaluation of the growth inhibitory effect of ceramic powder slurries on bacteria, and was more applicable than the conventional methods, such as the halo test.

/pdf/evaluation-of-growth-inhibitory-effect-of-ceramics-powder-5c0w9x85cs.pdf

Evaluation of Growth Inhibitory Effect of Ceramics Powder Slurry on Bacteria by Conductance Method

The effects of particlesize and heating temperature of magnesium oxide (MgO), calcium oxide (CaO), and zinc oxide (ZnO) powders on the antibacterial activities of their slurries were studied by the conductance method. An increase in particle size of the powders reduced their antibacterial activity. The variation of activity against Staphylococcus aureus was smaller than that against Escherichia coli, Salmonella typhimurium, and Bacillus subtilis. This difference depended on the shape of the bacteria, but not their character, such as the structure of the cell walls. The antibacterial activity of these powder slurries decreased with an increase in heating temperature of the powders. For the ZnO powder slurry, the decrease in antibacterial activity were much larger than those of the MgO and CaO powder slurries. It was suggested that these decreases in the antibacterial activity was concerned with stabilization of the surface of the powders heated at high temperature.

/pdf/effect-of-particle-size-and-heating-temperature-of-ceramic-3rqfnw7qjq.pdf

Effect of Particle-Size and Heating Temperature of Ceramic Powders on Antibacterial Activity of Their Slurries

The effects of magnesium oxide (MgO), calcium oxide (CaO), and zinc oxide (ZnO) powder slurries on spores of Bacillus subtilis were examined. The CaO and MgO powder slurries were able to kill the spores of B. subtilis in physiological saline. The efficacy of the CaO powder slurry was much higher than that of the MgO powder slurry. It was considered that the efficacy of the CaO powder slurry against the spores depended on effects of Ca2+ and some factors due to contact between spores and the CaO powders. When the spores and nutrients such as growth medium existed together, it was observed that the MgO, CaO and ZnO powder slurries exhibited antibacterial activity against spores of B. subtilis. There was no difference in sensitivity to the ceramic powder slurry between the vegetative cells and the spores of B. subtilis. Further, the supernatant of the ceramic powder slurries promoted the germination of the spores. Therefore, it was suggested that the ceramic powder slurries weakened a high dormancy of spores, and acted on the germinated spores.

Atsushi Hashimoto

Papers

Detection of Active Oxygen Generated from Ceramic Powders Having Antibacterial Activity

Evaluation of Growth Inhibitory Effect of Ceramics Powder Slurry on Bacteria by Conductance Method

Effect of Particle-Size and Heating Temperature of Ceramic Powders on Antibacterial Activity of Their Slurries

Effect of Ceramic Powder Slurry on Spores of Bacillus subtilis

Mutagenicity test of ceramic powder which have growth inhibitory effect on bacteria