Silver nanoparticle (SNP) has the advantages of high efficiency and broad spectrum, difficult to produce drug resistance, and high safety. However, there are still different views on the understanding of SNP antibacterial agents, and further in-depth research is continuing.
There are many examples of using silver as an antibacterial material in daily life. For example, when the skin is injured, the medical staff will use gauze made of silver wire to wrap the skin wound; using silver containers to hold food can extend the shelf life of food and so on. After scientists discovered antibiotics in the 1930s, silver-based antibacterial materials were ignored due to the widespread use of antibiotics. In recent years, due to the abuse of antibiotics, the problem of drug resistance caused by bacteria has been serious. Therefore, new low-cost and high-safety antibacterial materials represented by SNP have attracted people’s attention.
SNP has many excellent properties as an antibacterial material.
First, SNP is highly secure. Compared to silver ions, SNPs show strong antibacterial activity against microorganisms at very low concentrations (nanomoles or micromoles), while they are less toxic to mammals and have fewer complications.
Second, the durability is good. SNP can be supported on carriers such as chitosan, which continuously releases zero-valent silver ions, maintains a relatively stable silver concentration, and achieves the purpose of durable antibacterial.
Third, broad-spectrum antibacterial. SNP can effectively inhibit a variety of pathogenic bacteria, including Pseudomonas aureus, Staphylococcus, E. coli, Pseudomonas aeruginosa, and fungi such as dermatophytes, and can even kill HIV-1.
Fourth, it is not easy to develop drug resistance. SNP-treated bacteria are basically unable to survive, which can prevent bacteria from developing drug resistance.
Fifth, SNP also has the advantages of small toxic and side effects and convenient use.
However, when nano is used as an antibacterial material, it also exposes some problems, such as the life and safety problems caused by the accumulation and migration of silver. When silver is enriched to a higher concentration, it is more harmful to humans and mammals, and it will enter the mitochondria, embryos, liver and circulatory system with breathing. Some studies have pointed out that SNPs are more toxic than nanoparticles of metals such as aluminum and gold. Therefore, the scope and dosage of SNPs as antibacterial materials also deserve research and attention.
At present, the research mechanism of SNP is not sufficient. It is generally considered that SNP releases silver ions to play a role and induce the production of reactive oxygen species (ROS). Another study found that SNP itself directly exerts antibacterial effects and synergistically released silver ions play a role. The antibacterial principle of SNP generally recognized at this stage mainly affects the environment in which bacteria live, destroys cell walls, inhibits DNA replication, inhibits enzyme respiration, and inhibits other enzyme activities.
SNP exerts antibacterial effect by affecting the living environment of bacteria.
In the solution, under the synergistic effect of oxygen and proton, SNP releases silver ions or is oxidized by oxygen to form nano-silver oxide and then releases silver ions, which exerts antibacterial effect.
Some studies suggest that SNP itself has no effect on bacteria, and the inhibitory effect is due to the release of silver ions and strictly depends on the oxygen concentration.
Under aerobic conditions, both SNP and silver oxide particles showed strong antibacterial properties. However, metabolism such as bacterial aerobic respiration greatly reduces the oxygen content, resulting in a decrease in silver ion concentration and loss of antibacterial ability. The decrease in oxygen concentration in the environment has a huge impact on aerobic bacteria, directly inhibiting or even killing bacteria.
In addition, silver ions can be combined with nutrients in the system to reduce the concentration of elements necessary for bacterial growth.
It should also be shown that SNP induces oxygen to generate oxygen ions and water molecules to generate hydroxyl groups, which increases the consumption of oxygen and attacks the cell membrane. At higher concentrations of silver ions, silver ions can re-aggregate into zero-valent silver ions, so this process continuously consumes oxygen and exerts bacteriostatic effects.
SNPs exert an antibacterial effect by destroying the cell wall.
Silver ions and SNPs are positively charged on the cell membrane through electrostatic attraction with negatively charged bacterial proteins. Due to its high surface energy and dispersibility, chemical interactions occur between the SNP and the cell wall and destroy the integrity of the cell wall. This is particularly evident at the cell wall-enriched electronics site. Causes loss of normal cell wall functions such as nutrient penetration.
At the same time, SNP and silver ions act as membrane peroxidation inducers, interact with some proteins and phospholipids, and induce membrane damage or decomposition.
Some studies have reported that SNPs with a particle size of less than 20 nanometers are prone to sulfur-containing protein binding, interfere with protein functions and cause greater cell wall permeability. This shows that permeability change is an important way of antibacterial.
SNP exerts an antibacterial effect by inhibiting DNA replication.
SNPs break through cell walls and enter bacteria through membrane proteins and lipids (including changes in permeability and perforation). SNPs enter the bacteria and aggregate to form low-molecular-weight aggregates, and the cell wall is separated from the cell membrane, so that the DNA is aggregated and concentrated to avoid the damage of SNP. As a result, DNA stays between replications and the replication process cannot be completed. Or by blocking the electron transport system in the bacteria to enhance the stability of the bacterial DNA, the DNA cannot unravel the double helix, lose the ability to replicate, and reduce the speed of bacterial division.
SNPs and silver ions inhibit DNA replication and even lose replication ability by binding to DNA of the nucleus, pseudonucleus and mitochondria containing a large number of electron donor atoms.
SNP exerts an antibacterial effect by inhibiting the respiration of the enzyme.
Many studies have suggested that SNP’s inhibition of bacterial respiration is another way of bacteriostasis, including reducing the oxygen concentration inside and outside the bacteria, and directly affecting the enzymes related to breathing and ATP production.
SNP dissolves and releases silver ions to consume oxygen, and the solubility of oxygen in the bacterial environment and bacteria is reduced, which effectively inhibits bacterial respiration.
SNP exerts antibacterial effect by inhibiting the activity of other enzymes.
SNP enters the cell and is first attracted to the enzyme, proteome or organelle and lipid loaded with negative charge in the cell due to electrostatic attraction. Furthermore, it binds with electron donors (L-cysteine, etc.) such as sulfur, oxygen, and hydrogen in the enzyme, and even replaces metal ions in the enzyme, resulting in inactivation or even inactivation of the enzyme activity. In wound excipients, SNPs can inhibit the degradation of growth factors by inhibiting matrix metalloproteinases and improve the rate of wound healing.
In addition, silver ions and SNPs bind to nucleophilic groups such as amino acid residues (cysteine thio), amino, imidazole, phosphate, and carboxyl groups in functional proteins, changing the three-dimensional conformation of the enzyme, resulting in irreversible protein and normal metabolism of bacteria Unable to proceed.
In Gram-negative bacteria, SNP acts on phosphotyrosine peptides, and dephosphorylation of phosphotyrosine is observed. The protein phosphorylation process is related to signal transduction in bacteria. Based on this, it is concluded that SNP affects Signaling, which inhibits or interrupts bacterial growth.
In summary, SNPs are partially dissolved in solution to release silver ions. SNPs and silver ions are anchored to negatively charged functional groups on the bacterial cell wall. Functional proteins are affected by silver, and the bacterial cell wall and cell membrane structure change. Dysfunction, in particular, changes the permeability of the membrane, enters the cytoplasm, and causes the loss of bacterial nutrients. Silver damages the DNA structure in the cytoplasm, inhibits its replication and related activities such as respiratory chain enzymes, and eventually leads to bacterial inactivation. However, in the actual environment due to the presence of oxygen, SNP changes involve complex biochemical processes, including the aggregation of SNPs, the release of silver ions, the complexation of silver ions and organic matter, and the balance of dissolution and precipitation. the study.