Silver nanoparticles have an extremely significant role in vastly spread industries because of their remarkable characteristics like quantum confinement, high surface area, and small particle dimension.

Over 23% of all nanotechnology-based products, diagnostic and therapeutic applications implanted with silver nanoparticles (Wound healing and arthritic disease, etc.) are broadly famous because of their anti-inflammatory, anti-viral, antibacterial, antifungal, antiangiogenic effect, and anti-cancer agents, and AgNPs' anticancer activity mechanism, used in the textile fabrics and added as an antiseptic into the cosmetic products for overcoming the skin problems.

Introduction

There is the involvement of the AgNPs in biomedical applications. AgNPs aid in the targeted delivery of drugs, improving bioavailability, sustaining the gene or drug effect in the target tissues, and improving the stability. Silver nanoparticles are 1-100 nm in size. Although they are usually described as silver, some of them are made up of silver oxide as they possess a large ratio of the surface to bulk silver atoms. Silver nanoparticles that are commonly used are spherical but there is also common usage of the octagonal, diamond, and thin sheets. Generally, silver nanoparticles contain 15-20,000 silver atoms and they are smaller. As compared to their bulk parent materials, they possess distinct biological, chemical, and physical characteristics.

Overview of Silver Nanoparticles

The shape and size of the silver nanoparticles strongly influence the silver nanoparticle's catalytic, thermal, and optical characteristics. The coordination of a vast amount of ligands is permitted by their very large surface area.A huge amount of attention has been gained by the silver nanoparticles for a broad range of applications in different fields including biomedicine too. Moreover, silver nanoparticles are the most broadly utilized sterilizing nanomaterials in medical and consuming products because of their broad-spectrum antimicrobial capability, for example, personal care products, refrigerator surfaces, food storage bags, and textiles.

Properties of Silver Nanoparticles

Silver nanoparticles possess excellent and remarkable properties and their vast number of usages proves it. One can change their scattering and absorption properties by controlling the size, shape, and refractive index of the particle near the surface of the particle. The chemical and physical characteristics of the AgNPs include the type of reducing agents that are utilized for their production, cell type, ion release efficiency, particle reactivity in solution, dissolution rate, agglomeration, capping/coating, particle composition, particle morphology, shape, size distribution, size, and chemistry of the surface.

Applications of Silver Nanoparticles (AgNP)

Antibacterial Activity

Other than the antibiotics, AgNPs appear to be the substitutive antibacterial agent as they have the capability of overcoming the bacterial resistance to the antibiotics. Thus, developing AgNPs as the antibacterial agent is very significant. AgNPs are the potential antibacterial agent because of their crystallographic surface structure and large surface-to-volume ratios as compared to the other various promising nanomaterials. Sondhi and Salopek-Sondhi reported a seminal paper in which they displayed the AgNPs antimicrobial activity against E. coli, in which the AgNPs-treated E. coli cells displayed the AgNPs accumulation in the cell wall and pits formation in the cell walls of bacteria, eventually resulting in cell death.

As compared to the larger particles, a more effective and efficient antibacterial activity was shown by the smaller particles with a larger surface-to-volume ratio in the same E. Coli strain. Remarkable antibacterial activity was shown by the hydrogel-silver nanocomposites against E. coli in comparison to the AgNPs. In addition, AgNPs are capable of destroying the bacterial membrane's permeability by generating various gaps and pits, which indicates that the bacterial cell membrane's structure could be damaged by the AgNPs. Out of all the nanoparticles that are tested, AgNPs had the strongest antibacterial activity among the numerous nanomaterials. Silver's antimicrobial characteristics were interestingly investigated by Khurana et al. based on its surface and physical characteristics against S. sonnei, P. Vulgaris, B. megaterium, and S. aureus.

Anti-Inflammatory Activity

Inflammation is an early immunological response by tissue against the foreign particles, which is supported by the immune system's activation, pro-inflammatory cytokines' increased production, and release of the chemotactic substances like TGF-β, TNF-α, interleukin-1 (IL-1), prostaglandins, and complement factors. Effective anti-inflammatory agents need to be found for overcoming the inflammatory action. A significant role is played by the AgNPs in the anti-inflammatory field among various anti-inflammatory agents. Majorly reduced inflammation of the colon was seen in the rats that were treated orally with 40 mg/kg of nanocrystalline silver (NPI 32101) or intra-colonically with 4 mg/kg of nanocrystalline silver (NPI 32101). Enhanced cosmetic appearance and fast healing were shown by the mice that were treated with the AgNPs in a dose-dependent manner. Modulation of fibrogenic cytokines, reduction in the inflammation of the wound, and major antimicrobial characteristics were displayed by the AgNPs.

Antifungal Activity

Immunosuppressed patients have more chances of getting fungal infections, and overcoming the fungi-mediated diseases is a tedious process, as there are not many Antifungal drugs available right now. Thus, there is an urgent and inevitable need of developing antifungal agents, that should be non-toxic, biocompatible, and friendly to the environment. A significant role is played by the AgNPs at this juncture as anti-fungal agents against numerous diseases that are caused by fungi. Antifungal activity is displayed by the biologically synthesized AgNPs at 15 mg of concentration against numerous phytopathogenic fungi, including Curvularia lunata, Botrytis Cinerea, Rhizoctonia solani, Macrophomina phaseolina, Sclerotinia sclerotiorum, and Alternaria alternata. Relatively, strong antifungal activity was displayed by the AgNPs synthesized by Bacillus species at 8 μg/mL of concentration against the plant pathogenic fungus Fusarium oxysporum.

Antiviral Activity

Development of the anti-viral agents is important as viral mediated diseases are common and turning more famous and prominent in the world. A significant aspect of antiviral therapy is the mechanisms of the AgNPs’ antiviral activity. Remarkable interactions with viruses and bacteria based on certain shapes and size ranges are possessed by the AgNPs. There was an evaluation of the antiviral activity nano-Ag incorporated into polysulfone ultrafiltration membranes (nAg-PSf) against MS2 bacteriophage. The evaluation showed that it was the increased membrane hydrophilicity that caused major antiviral activity. Effective inhibitory activities are displayed by the AgNPs against hepatitis B virus (HBV) and human immunodeficiency virus (HIV). There were investigations on the AgNP's antiviral action. However, it is seen in various studies that the virus's viability can be inhibited by the AgNPs, however, their antiviral activity exact mechanism is still not known well.

Anticancer Activity

1 in 3 people can develop cancer in their lifetime. However, currently, there is the utilization of various chemotherapeutic agents for different types of cancers, with huge side effects, and administering chemotherapeutic agents via IV infusion is a slow process. Thus, developing technologies for avoiding systemic side effects is indispensable. It was of interest to many researchers that they develop the nanomaterials at this juncture as an alternative tool for creating the formulations that can specifically target the tumor cells. AgNPs' molecular mechanism was investigated by Gopinath et al. It was observed that under conditions, the programmed cell death was concentration-dependent. It was observed in these experimental conditions that not only apoptosis was induced by the AgNPs, but they also sensitized the cancer cells.

There were studies of the starch-coated AgNPs anticancer characteristic in the human glioblastoma cells (U251) and normal human lung fibroblast cells (IMR-90). Increased oxidative stress, decreased metabolic activity and cell viability, and alterations in the morphology of the cells are induced by the AgNPs, resulting in mitochondrial damage and reactive oxygen species (ROS) increased production, ending with damage to the DNA. Cancer cell morphology analysis tells that cell death can be induced by the biologically made AgNPs very majorly.

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AgNPs’ Diagnostic, Biosensor, and Gene Therapy Applications

It is because of the sharper and stronger plasmon resonance of the silver that it performs a major role in imaging systems. The smaller size of the AgNPs is the reason for their usage in this field, as it increases the acoustic reflectivity, ultimately resulting in clearer image creation and an increase in the brightness. Nanosilver is also used as a drug carrier and diagnosing and treating cancer. Moreover, it can locate the cancer cells, absorb light and destroy the targeted cancer cells selectively through photothermal therapy.

Using AgNPs as a Therapeutic Approach for The Treatment of Cancer

Multifunctional Nanoparticles were made by Khlebtsov et al. They promoted cell death in the HeLa cervical cancer cells. It was concluded that one can utilize AgNPs as the nanocarriers for some particular drugs for treating cancer. There has been recent usage of the photo-based therapeutic approaches by the nanomaterials to diagnose, treat, and prevent cancer. Nanostructures can destroy the cancer cells better than the non-cancer cells at low irradiation power density. AgNPs are an appropriate promising agent for inhibiting cancer cell growth by using numerous mechanistic approaches.

AgNPs’ Wound Healing Applications

S.aureus, P. aeruginosa, and E. Coli’s microorganism growth were repressed by the silver nanoparticles made by utilizing the ultraviolet irradiation within the silver nanoparticles. No vital influence was seen on the viability of the cell by the AgNPs containing hydrogels on the HDFa cells. A positive result was exerted by the animal model because of their antimicrobial potential as AgNPs hydrogel was being observed for the wound healing action. A novel therapeutic direction was also provided in clinical observation for the treatment of wounds. Differentiation of the fibroblasts into myofibroblasts was driven by the AgNPs and they induced wound contraction too, thus increasing the effectiveness of the wound healing.

Silver nanoparticles' positive effects reduced the inflammation of the wound with modulation in the urinary organ and liver functions throughout skin wound healing through their antimicrobial characteristics. A responsibility is played by the AgNPs in epidermal reepithelialization and dermal contraction during wound healing, contributing to the wound closure’s increased rate. Fungus Aspergillus niger was used to extracellularly prepare the AgNPs which are reported for the modulation of the cytokines that are involved in the healing of wounds within the excision rat model. It was observed that there was a significant reduction in the wound-healing in 3.35 days of median time for the AgNPs that are incorporated onto the dressings and cotton cloth and there was also an enhancement of the microorganism clearance from the infected wounds. Antimicrobial characteristics are possessed by the silver nanoparticles, inflicting reduction in the inflammation of the wound and fibrogenic cytokines’ modulation.

Textile Applications of Silver Nanoparticles

In the textile industries, there is commercial usage of the nanomaterials by their coating with fiber or incorporation into the fiber, for example, one can find the usage of the silver nanoparticles in socks, undergarments, sporting clothes, and T-shirts.

UV Rays Blocking Textile

As compared to the organic UV blockers, the inorganic UV blockers are more beneficial because they are chemically stable and non-toxic on their exposure to both UV and high temperatures. Generally, the inorganic UV blockers are semiconductor oxides, for instance, Al2O3, SiO2, ZnO, and TiO2. Zinc oxide (ZnO) and titanium dioxide (TiO2) are the most commonly utilized semiconductor oxides among these semiconductor oxides. It was resolute that the nano-sized Zinc Oxide and titanium dioxide are relatively more efficient when it comes to the absorption and scattering of the UV radiation and offer better protection against the ultraviolet rays. This is because as compared to the conventional materials, a larger surface area per unit mass and volume is possessed by the nanoparticles, resulting in the increment ineffectively blocking the UV radiation.

Many researchers prefer the idea of using nanotechnology for the application of UV blocking treatment to the fabric. The sol-gel method develops the UV blocking treatment for the cotton fabrics. According to the recent studies on UV blocking, a remarkable UV protection factor (UPF) rating is possessed by the fabric that was treated with zinc oxide nanorods. Numerous procedures to apply the nanoparticles on the surface of the fabric can be done to further enhance these effects. Significantly, the fabric's only right (face) side is exposed to the rats and thus, nanoparticles need to cover this surface alone for good UV protection. An alternate method to the application of the nanoparticles is using the nanoparticles to spray the fabric surface (utilizing a spray gun and compressed air).

Medicinal Textiles and Devices

Corynebacterium is a sweat microorganism and high resistance is expressed towards it by the AgNPs made utilizing A. dubious fabricated on the cotton cloth and perspiration pad samples. Antimicrobial activity is displayed against the antibacterial drug activity of the gauze fabric discs that are incorporated with the AgNPs, made from the inexperienced mature thalli of Anthoceros against the Pseudomonas aeruginosa. Minimum bactericidal concentration (MBC) is displayed by the Curcuma longa tuber dust enveloped silver nanoparticles at 50 mg/L for Escherichia coli BL-21 strain. Sterile water is used for the immobilization into the fabric and it specifies higher antiseptic activity as compared to the polyvinylidene fluoride immobilized cloth. Azadirachta indica’s incorporation made the silver nanoparticles into the cotton cloth, leading to the antibacterial drug effect, against E. Coli.