The Properties and Applications of Nanosilver

  • Abstract: Nano-silver is a single element of metallic silver with a particle size of nanometer. The particle size of Nano-silver is mostly around 25 nm, and the performance of nano-silver is directly related to its particle size. Moreover, the surface effects and quantum size effects of nano-silver particles make them exhibit excellent physical and chemical properties in the fields of electricity, optics, surface catalysis and sensing. Not only that, the emergence of nanotechnology has made a qualitative leap in the bactericidal ability of silver in the nano state. Very small amount of nano silver can produce a strong bactericidal effect, killing more than 650 kinds of bacteria in a few minutes, broad-spectrum sterilization and without any drug resistance; it can promote the healing of wounds, the growth of cells and the repair of damaged cells without any toxic reaction, and no stimulating reaction to the skin. This opens up a wide range of applications for the widespread application of nano-silver antibacterial. The future is the latest generation of natural antibacterial agents. Nano-silver has broad application prospects as dielectric materials, electrode materials, optical labels, light-sensitive materials, biosensors, and Raman-reinforced substrates. This article focuses on how nanosilver is prepared, the antibacterial properties of nanosilver and its wide application.

    Keywords: nanosilver, microbe, antibacterial, application

    Preparation of Nano Silver

    The preparation methods of nano silver currently reported mainly include chemical methods and physical methods. The physical method refers to the direct conversion of silver into nanoparticles by various dispersion techniques, such as evaporative condensation, ion sputtering, high-energy mechanical ball milling, laser sputtering, etc.; chemical method is to reduce silver ions to form nanoparticles by chemical reaction. Common methods include liquid phase chemical reduction, electrochemical reduction, photochemical reduction, and molecular self-assembly. However, these methods have some shortcomings: the physical method requires high equipment and equipment, the production cost is high, and the energy consumption is high; the chemical method requires the use of more reducing agents, and these compounds are expensive, highly toxic, and highly polluted. With the popularization of the concept of green chemistry, the synthesis of nano-silver is also developing in a non-toxic and environmentally friendly direction.

    In addition, it has to be mentioned that the emerging microbial synthesis method is used to prepare nanosilver. In general, microbial synthesis methods mainly use biological materials such as microorganisms and plants. Compared with traditional physical and chemical synthesis methods, biosynthesis methods have many advantages, such as wide sources of materials, low prices, and mild and controllable reaction conditions. This is a clean, non-toxic, environmentally friendly and sustainable synthetic method that has gradually become a research hotspot in the field of nano synthesis. To date, it has been found that many species, including prokaryotes and eukaryotes, have the ability to synthesize nanosilver, such as single-cell bacteria, yeast, multicellular fungi, and have the ability to synthesize nanosilver either intracellularly or extracellularly.

    • Bacteria

    The first condition for the synthesis of nanosilver using microorganisms is that the microorganism needs to have some tolerance to silver. The advantage of using bacteria to synthesize nanosilver is that it is easy to operate, and genetic engineering can be used to change or improve the synthesis efficiency and yield.

    • Yeast

    Yeast has been used for intracellular synthesis of nano crystals for many years. As reported in 1988, Candida glabrata was placed in a medium containing Cd, and CdS quantum dots were formed in the cells. However, yeast has been reported in recent years that can be used for nano silver synthesis.

    • Fungus

    The use of fungus for the synthesis of nanosilver has been a method developed in recent years and has made great progress. Compared with bacteria and yeast, fungi have the advantage of secreting large amounts of enzymes, and the separation process is simple. The preparation of monodisperse nano crystals can be achieved by using enzymes secreted by fungi, and the control of crystal morphology can be realized. Among them, Fusarium, Aspergillus and Penicillium have great potential in synthesizing nano silver.

    • Actinomycetes

     Compared with bacteria, actinomycetes have been studied late for nanosilver synthesis. The marine actinomycetes isolated by the famous scholar Prakasham synthesized nano silver. Zinicovscaia et al. isolated an actinomycete Streptomyces glaucus 71MD from soybean rhizosphere soil. For the first time, they delved into the physiological and biochemical properties of the microorganism and applied it to nanosilver synthesis.

    The Biggest Advantage: Antibacterial Properties

    The antibacterial properties of nanosilver mainly have the following characteristics:

    • Broad spectrum antibacterial properties

    The nano-silver particles directly enter the bacteria to bind to the oxygen metabolism enzyme (-SH), so that the unique mechanism of suffocation of the bacteria can kill most of the bacteria, fungi, molds, spores and other microorganisms in contact with them. It has been found by eight major domestic authorities that it has comprehensive antibacterial activity against drug-resistant pathogens such as resistant Escherichia coli, Staphylococcus aureus, resistant Pseudomonas aeruginosa, Streptococcus pyogenes, Enterococcus faecalis, anaerobic bacteria, etc. Bactericidal effects on burnt scalds and common bacteria on the wound surface such as Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans and other G+ and G- pathogenic bacteria; it causes Chlamydia trachomatis, causing sexually transmitted diseases Neisseria gonorrhoeae also has a strong bactericidal effect. 

     

     

     

    An antibiotic kills about six pathogens, while nanosilver kills hundreds of pathogenic microorganisms. Nano-silver can not only kill bacteria, fungi, trichomoniasis, mycoplasma, chlamydia, gonococcus, but also has strong bactericidal effect, and has the same killing effect on antibiotic-resistant bacteria!

    • Strong bactericidal properties

    According to research, Ag can kill more than 650 kinds of bacteria in a few minutes. After binding to the cell wall or cell membrane of the pathogen, the nano silver particles can directly enter the cell body and rapidly bind to the sulfhydryl group (-SH) of the oxygen metabolism enzyme, so that the enzyme is inactivated, and the respiratory metabolism is blocked to cause suffocation and death. The unique bactericidal mechanism allows the nano-silver particles to quickly kill pathogenic bacteria at low concentrations.

    • Strong permeability

    The nano silver particles have excellent permeability and can quickly penetrate into the subcutaneous 2mm sterilization, and have good bactericidal effects on common bacteria, stubborn bacteria, drug-resistant bacteria and deep tissue infection caused by fungus.

    • Repairable regenerability

    Nano-silver can promote wound healing, promote the repair and regeneration of damaged cells, detoxify the muscles, antibacterial and anti-inflammatory to improve the microcirculation of tissues around the wound, effectively activate and promote the growth of tissue cells, accelerate the healing of wounds and reduce the formation of scars.

    • Antibacterial durability

    Nanosilver is a non-antibiotic bactericide. Nano-silver can kill various pathogenic microorganisms, which is stronger than antibiotics. Due to its unique antibacterial mechanism, nano-silver particles of 10 nm can quickly kill bacteria directly and make them lose their reproductive ability. Therefore, the next generation of drug resistance cannot be produced, and it is possible to effectively prevent repeated attacks from being cured due to drug resistance.

    Several Applications of Nano Silver

    Nano silver has broad application prospects and can be used as dielectric materials, electrode materials, optical labels, light sensitive materials, biosensors, anti-infective wound repair materials, and additives for water treatment membranes.

    • Nano silver electrochemical sensor

    In the nano-silver electrochemical sensor, nano-silver mainly functions as a modified electrode. Tests have shown that nano-silver can be modified to the surface of the electrode by means of dispensing. Electrochemical impedance analysis was performed using [Fe(CN)6] as a probe, and the impedance characteristics during electrode construction were studied by electrochemical impedance spectroscopy. The figure shows the impedance map of the bare electrode (b) and the nano-silver modified electrode (a). 

    It can be seen from the figure that the bare electrode and the nano-silver modified electrode have obvious semicircles in the high frequency region, which represents the resistance of the electrode. The diameter of the semicircle of the bare electrode is relatively large, and the diameter of the semicircle of the silver sol is relatively small, indicating that the silver ion has been successfully adsorbed on the surface of the electrode, and the moving speed of the electron is accelerated, so that the impedance value of the electrode is drastically reduced. It has been proved that the nano-silver modified electrode has good stability and reproducibility for the detection of sparfloxacin, so it can be used for the detection of the actual sample of sparfloxacin.

     

    • As a new antibacterial agent

    Silver is used in the treatment of burns and various bacterial infections in various forms such as metallic silver, silver nitrate, and silver sulfadiazine. With the discovery and application of antibiotics, the application of these silver complexes has dropped significantly. However, in recent years, nanotechnology has greatly changed the chemical, physical and optical properties of metals due to the adjustable metal size to the nanometer scale. Nano scale metallic silver has become a potential antibacterial agent. Due to the occurrence of antibiotic resistance, the application of nanosilver has broad prospects.

    Due to its unique physical and chemical properties, nano-silver particles are a good choice for new antibacterial agents. The antibacterial properties of nanosilver particles are superior to other forms of silver, mainly due to their large surface area for better contact with microorganisms. Moreover, the nanoparticles can adhere to the cell membrane and can also penetrate into human bacterial cells. The bacterial cell membrane has a sulfur-containing protein, and the nano-silver particles are capable of interacting with these proteins in the cell while also interacting with the phosphorus-containing compound, such as DNA. When the nanosilver particles enter the bacterial cells, a low molecular weight region can be formed in the center of the bacteria, and the bacteria aggregate to the region to protect the DNA from silver ions. Nano-silver particles can effectively cause cell death. Nano-silver particles can also release silver ions into bacterial cells to enhance bactericidal activity. In addition, nano-silver particles are widely used in various forms, such as wound dressings, coatings for medical devices, nano-silver impregnated fabrics, and the like. Nano-silver particles can treat burn wounds with good appearance and promote wound tissue healing.

    • As an important component of water treatment membranes

    The water treatment membrane is a porous material with selective separation function. The separation of the different components of the sewage can be separated, purified and concentrated by the selective separation of the water treatment membrane. The pore size of the water treatment membrane is generally micrometer, and the current water treatment membrane has the following are: microfiltration membrane (MF), ultrafiltration membrane (UF), nano filtration membrane (NF), reverse osmosis membrane (RO), electrodialysis membrane (ED) and the like. The water treatment membrane is mainly used for seawater desalination and brackish water desalination, pure water treatment, industrial wastewater treatment, sewage reuse, drinking water treatment and the like. Compared with traditional water treatment technology, membrane technology has the advantages of energy saving, low investment, simple investment and high processing efficiency.

    Although the membrane separation technology has the advantages of high efficiency, energy saving, environmental protection, simple process and easy control, there are also problems in the process of water treatment, that is, the pollution of the water treatment membrane. Membrane fouling will not only lead to a decrease in water flux, but also shorten the service life of the membrane and increase the cost of water production, thus restricting the development of membrane technology. One way to solve this problem is to combine nanosilver with a water treatment membrane to improve the antibacterial and antifouling properties of the membrane. As an emerging inorganic material, nano silver particles can effectively reduce the surface roughness of the film and improve the hydrophilic property of the polymer film when it is well dispersed in the ultrafiltration membrane, nano filtration membrane or reverse osmosis membrane. It has great significance and economic value to give the water treatment membrane a strong antibacterial ability, can effectively prevent microbial contamination, and prevent the formation of biofilm on the surface of the membrane.

    It is expected that the hybrid antibacterial film formed by the combination of the nano silver particles and the water treatment film has a good application prospect in the field of sewage treatment and water purification. However, it should be noted that there are still many problems that cannot be ignored in the research and application of nano-silver antibacterial film. For example, the nano-silver is easily lost during long-term operation, which leads to the decline of its antibacterial performance and environmental pollution problems. . Therefore, the development of environmentally friendly antibacterial agents and the further improvement of the antibacterial sustainability of water treatment membranes are the future research directions.