Nanosilver: new ageless and versatile biomedical therapeutic scaffold

Abstract

Silver nanotechnology has received tremendous attention in recent years, owing to its wide range of applications in various fields and its intrinsic therapeutic properties. In this review, an attempt is made to critically evaluate the chemical, physical, and biological synthesis of silver nanoparticles (AgNPs) as well as their efficacy in the field of theranostics including microbiology and parasitology. Moreover, an outlook is also provided regarding the performance of AgNPs against different biological systems such as bacteria, fungi, viruses, and parasites (leishmanial and malarial parasites) in curing certain fatal human diseases, with a special focus on cancer. The mechanism of action of AgNPs in different biological systems still remains enigmatic. Here, due to limited available literature, we only focused on AgNPs mechanism in biological systems including human (wound healing and apoptosis), bacteria, and viruses which may open new windows for future research to ensure the versatile application of AgNPs in cosmetics, electronics, and medical fields.

Keywords: antimicrobial properties; biomedical applications of AgNPs; synthesis of AgNPs; theranostics.

Figure 1

Overall view of (A) synthesis methods, (B) biological properties, and (C) biomedical applications and toxicity of AgNPs. Abbreviation: AgNPs, silver nanoparticles.

Figure 2

Chemical synthesis of AgNPs. Abbreviation: AgNPs, silver nanoparticles.

Figure 3

Biogenic or green synthesis of AgNPs. Abbreviation: AgNPs, silver nanoparticles.

Figure 4

Polysaccharides-based synthesis of AgNPs in which polysaccharides (cellulose), alcohol, and aldehyde groups act as stabilizing agents. Abbreviation: AgNPs, silver nanoparticles.

Figure 5

Graphical abstract representing the synthesis (green) and the biocidal potential of AgNPs against various microbes. Abbreviation: AgNPs, silver nanoparticles.

Figure 6

Mechanism of action of AgNPs in a biological system. (A) AgNPs antiviral mechanism. After attachment to host cell, the virus inserts its genetic material into the cell. Silver particles bind to the genetic material and block its replication which ultimately leads to translational inhibition, and in this way, viral growth is inhibited. (B) Wound healing and antibacterial mechanism of AgNPs. Although not reported in the literature, we assume that AgNPs may react with free oxygen in the wound portion followed by its ionization. This ionized active silver may regulate FOXO1 which is a transcription factor stimulating wound healing molecule, TGF-β1. Furthermore, active silver has also been reported to generate ROS. In the eukaryotic system, the ROS activate JNK and p53 proteins which induce Bax proteins to migrate to the mitochondrial surface resulting in cytochrome C release from mitochondria which subsequently results in PARP cleavage. This phenomenon leads to apoptosis. The antibacterial mechanism of AgNPs starts with adhesion of AgNPs to bacterial cell followed by pit formation through which AgNPs enter the cell. These AgNPs then bind to nuclear material residing inside the bacteria. This leads to transcriptional and translational disruption and subsequently leads to ROS generation, which results in antibacterial activity. Abbreviations: AgNPs, silver nanoparticles; ROS, reactive oxygen species.