Several mechanisms have been proposed to explain the inhibitory effect of silver nanoparticles on bacteria. It is assumed that the high affinity of silver towards sulfur and phosphorus is the key element of the antimicrobial effect. Due to the abundance of sulfur-containing proteins on the bacterial cell membrane, silver nanoparticles can react with sulfur-containing amino acids inside or outside the cell membrane, which in turn affects bacterial cell viability. It was also suggested that silver ions (particularly Ag+) released from silver nanoparticles can interact with phosphorus moieties in DNA, resulting in inactivation of DNA replication, or can react with sulfur-containing proteins, leading to the inhibition of enzyme functions. The general understanding is that Ag nanoparticle of typically less than 20 nm diameters get attached to sulfur-containing proteins of bacterial cell membranes leading to greater permeability of the membrane, which causes the death of the bacteria .
The inhibitory activity of TiO2 is due to the photocatalytic generation of strong oxidizing power when illuminated with UV light at wavelength of less than 385 nm . Hydroxyl radicals (• OH) and reactive oxygen species (ROS) produced on the illuminated TiO2 surface play a role in inactivating microorganisms by oxidizing the polyunsaturated phospholipid component of the cell membrane of microbes. OH radicals are about a thousand or possibly ten thousand times more effective than common disinfectants such as chlorine, ozone and chlorine dioxide for E. coli inactivation .
It has been suggested that nanostructured TiO2 on UV irradiation can be used as an effective way to reduce the disinfection time, eliminating pathogenic microorganisms in food contact surfaces and enhance food safety .
TiO2 is non-toxic and is approved by the American Food and Drug Administration (FDA) for use in human food, medicines, cosmetics, and food contact materials. Currently, there is great interest in the self-disinfecting feature of TiO2 to meet the hygienic design requirements on food processing and packaging surfaces .
Among the various metal oxides studied for their antibacterial activity, zinc oxide nanoparticles have been found to be highly toxic. Moreover, their stability under harsh processing conditions and relatively low toxicity combined with the potent antimicrobial properties favours their application as antimicrobials. Many studies have shown that some NPs made of metal oxides, such as ZnO NP, have selective toxicity to bacteria and only exhibit minimal effect on human cells, which recommend their prospective uses in agricultural and food industries.
There are several mechanisms which have been proposed to explain the antibacterial activity of ZnO nanoparticles. The generation of hydrogen peroxide from the surface of ZnO is considered as an effective mean for the inhibition of bacterial growth. It is presumed that with decreasing particle size, the number of ZnO powder particles per unit volume of powder slurry increases resulting in increased surface area and increased generation of hydrogen peroxide. Another possible mechanism for ZnO antibacterial activity is the release of Zn2+ ions which can the damage cell membrane and interact with intracellular contents .
• Low toxicity of silver on human cells, long biocide action, high thermal ability and low volatility.
• Broad spectrum of biocide activity against 650 bacteria, mushrooms and viruses.
• Effective antifungal agent against a broad spectrum of common fungi.
• Antiviral agent against HIV-1, hepatitis B virus, respiratory syncytial virus, herpes simplex virus type 1, and monkeypox virus.
• Nanosilver particles have higher antiviral activity than silver ions.
•Medical textiles for maintaining the sterility of equipment and surfaces
• Wound dressings.
• Water treatment.
• Medical implants.
• Medical catheters.
• Dental materials.
Titanium dioxide nanoparticles
• Very active for microbial destruction, even under limited UV light available in regular fluorescent lights. The bactericidal and fungicidal effects of nano-TiO2 on, for example, Escherichia coli (E. coli), Staphylococcus aureus, and Pseudomonas putida have been widely reported.
• Air and water purification.
• Hospitals and other bacteria prone environments.
• Medical implants
• Food processing.
• Construction (i.e. concrete blocks, plasters, windows and ceramic tiles).
Zinc oxide nanoparticles
• Display high anti-infective activity, improved wound healing, and higher epithelialization rates.
• Strong anti-microbial activity against Gram-positive bacteria.
• Anti-microbial activity against spores that are resistant to high temperature and high pressure.
• Anti-microbial properties are believed to be due to OH radicals, which result from defects in their crystal structure. However, the exact mechanisms of the antibacterial action have not yet been clearly identified.
• Medical bandages and wound dressings.
• Food contact surfaces.
• Water treatment.
 Vittal, R.R., Aswathanarayan, J.B., 2011, Nanoparticles and their potential application as antimicrobials, FORMATEX, 197-209.
 Chawengkijwanich, C, Hayata, Y., 2008, Development of TiO2 powder-coated food packaging film and its ability to inactivate Escherichia coli in vitro and in actual tests, International Journal of Food Microbiology, 123, 288–292.
 Market report, "The Global Market for Antimicrobial, Antiviral and Antifungal Nanocoatings 2020".