1. Introduction
Nanotechnology recognizes, produces, and applies materials in dimensions smaller than 1000 nanometers at the atomic, molecular, and macromolecular scales [1]. Silver nanoparticles are clusters of silver atoms that range from 1 to 100 nanometers. The properties of nano-sized silver are very different from the properties of this element in bulk size. Silver nanoparticles’ physical, optical, thermal, chemical, electrical, mechanical, and biological properties are unique [2]. Using nano-silver with different materials such as fibers, dyes, polymers, ceramics enables us to produce products that make our environment free of germs while not harming the environment [1]. Therefore, this review article aimed to summarize the antimicrobial application mechanisms of silver nanoparticles in different shapes, sizes, and concentrations on the cells of other organisms (Figure1). 2. Materials & Methods
PubMed, ISI, Web of Science, Scopus, ISC, and Google Scholar databases were used to collect and summarize data. Research papers using the MeSH model were: fungi, viruses, bacteria, and antimicrobial properties of silver nanoparticles. Ethical considerations: Ethical principles in writing the article are per the instructions of the National Ethics Committee and the COPE regulations.
3. Result
 The antimicrobial effect of silver nanoparticles depends on the concentration, shape, and diameter of the nanoparticles, as well as the time of impact and the type of microorganism. The molecular mechanism of these nanoparticles has been through oxidative stress. The mechanism of inhibitory action of silver ions on microorganisms is the loss of DNA replication ability inactivation of the expression of ribosomal subunit proteins and other bacterial cell proteins and enzymes necessary for ATP production. The effect of silver ions is primarily on the function of membrane-bound enzymes such as critical enzymes in the respiratory chain. Thus, similar cellular mechanisms can cause death in prokaryotes, fungi, and eukaryotes (Figure 2). 4. Discussion & Conclusion
Using silver nanoparticles as a new antimicrobial agent has recently attracted the attention of many researchers. Researchers have proven the ability of silver nanoparticles to fight spoilage and pathogenic microorganisms. Numerous studies were conducted on possible reactions between the nanoparticles and macromolecules of living organisms. The difference between the negative charge of the microorganism and the positive charge of the nanoparticle acts by creating adsorbent electromagnetic bands between the microbe and the nanoparticle, causing the nanoparticle to attach to the cell surface, resulting in cell death. Eventually, many of these contacts lead to the oxidation of the surface molecules of the microbes and their rapid extinction. The ions released from the nanomaterials are likely to react with the thiol groups of SH surface proteins of bacterial cells. Some of these bacterial cell membrane proteins transport minerals from the wall surface. Nanomaterials cause inactivation and impermeability of cell membranes by acting on these proteins. The loss of membrane permeability eventually leads to cell death. The presence of silver and sulfur ions in compact electron granules in the bacterial cytoplasm after treatment with silver nanoparticles has been observed, which indicates interaction with nucleic acids and leads to disruption of DNA molecule amplification. Nanomaterials also delay bacterial cell adhesion and biofilm formation, which prevents a group of bacteria from stabilizing and multiplying. Silver nanoparticles have antimicrobial properties on most microorganisms, so it can be said that variables, such as the type of microorganism, contact time, concentration, shape, and diameter of silver nanoparticles, factors affecting the occurrence of apoptosis in different types of cells, including prokaryotes and fungi, eukaryotes, and viruses. Considering the biocompatibility of these nanoparticles in specific diameters and concentrations and the reduction of side effects, they can be used as alternatives to standard drugs, such as some antibiotics and antifungals, shortly.

Ethical Considerations
Compliance with ethical guidelines
Ethical principles have been observed in writing the article.

Funding
This article has no financial support.

Authors' contributions
Both authors contributed to the review and writing of the article.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgements
We would like to thank all the researchers and authors of the articles whose research results were used in this study.


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