Antibacterial agents are very important in various industry, such as food packaging, medicine, water disinfection, and textile industry. The antibacterial application requires the compound to kill bacteria locally or slow down their growth but not being toxic to surroundings. The traditional antibacterial organic compounds possess some intrinsic disadvantages, such as non-stable in certain conditions and toxic to the human body. Therefore, the interest in metallic nanoparticles and metal oxide nanoparticles has been increasing in last several decades. Inorganic nanoparticles, especially metallic nanoparticles and its oxides have attracted great interests in the antibacterial application. Common used nanoparticles as antimicrobials include but not limited to Ag, MgO, TiO2, ZnO, Fe3O4, Au, CuO, Al, Bi, Carbon-based nanoparticles. Even at low concentrations, these nanoparticles have exhibited strong antibacterial activity due to their unique chemical-physical properties and high surface area to volume ratio. Another advantage is that they are more stable in extreme conditions such as high temperature and pressures with none or little toxic effect on food.
The exact antibacterial mechanisms of nanoparticles remain unclear. However, some possible explanations attributed to the antimicrobial activity of these nanoparticles have been studied by researchers. These proposed mechanisms include the interaction of nanoparticles with microorganisms, the release of antimicrobial metabolic ions, the generation of ROS, alteration of bacterial morphology, the disorganization to bacterial cell walls, the damage to the integrity of the bacterial cell, and intracellular content leakage.
Figure 1. Mechanisms for the antimicrobial effect of nanoparticles
1. Food Packaging
Foodborne diseases have been a critical issue and affect global health, trade and the economy. In order to control foodborne pathogens, provide safety, and the quality of food, new techniques in food packaging have attracted tremendous attention. Antimicrobial packaging is one of the new functioning active packaging, which interacts with the product and inhibits the microorganisms’ growth. Organic compounds such as organic acids, essential oils, lysozymes, and bacteriocins have been tested for antimicrobial food packaging but their application was limited due to some disadvantages, such as their sensitivity to the processing conditions and the development of microorganism resistance. On the contrast, inorganic nanoparticles have been considered as a novel and safe alternative reagent for food package owing to its none or little toxic effect. For example, the U.S. Food and Drug Administration has listed ZnO as generally recognized as safe (GRAS) material. The silver nanoparticles and silver coatings have also been studied in “smart” packaging. It is designed for sensing specific pathogens developing specific gases in the food or from food spoiling. By detecting the biochemical or microbial changes in the food, this silver-based packaging may also be used as tracing device for food safety or to avoid counterfeit.
2. Wounds Antiseptics
Infections during surgical operations or on the wounds are of the most serious healthcare problems and may lead to deaths. The use of nanoparticles as antiseptics and a way to disinfect wounds is more effective than existing techniques due to the unique properties of the nanoparticles. For example, nanoparticles can penetrate deeper to the area affected by surgery owing to its tiny size to enter the skin via hair follicles. The inhibitory and bactericidal effects of nanoparticles can be beneficial in the prevention and treatment of bacterial colonized/infected wounds. The antimicrobial, antifungal effect of nanoparticles can also prevent the biofilm formation and used as wound dressing. Silver, gold, copper, carbon, titanium and zinc oxide nanoparticles have shown a potential antibacterial effect on skin disinfection and therapeutic effects on wound healing. Carbon-based nanoparticles, especially graphene-based nanoparticle, are a novel and promising antiseptics nanomaterials. A recent study has shown that the graphene quantum dots-Band-Aids showed good antibacterial property and helped with in actual wound disinfection in mice models. Moreover, by reducing wound bioburden, treating local infection, and preventing systemic spread, clinical evidence has shown that the usage of silver nanoparticle dressing can promote wound healing indirectly.
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