Various researchers have been focused on the synthesis of silver nanoparticles (SNPs) owing to their widespread benefits in various fields including material sciences, biotechnology, medical sciences, engineering, etc. Biological applications and toxicity of SNPs are greatly dependent on their method of synthesis, experimental model species, duration and dose regime, etc. Green-synthesis is a commonly used methodology for synthesis medical grade SNPs that has minimal to nil toxicity and good biocompatibility in various animal models and human beings. Therefore, a number of SNPs technologies and products have been licensed and commercialized in the consumer markets for human application and treatment of various medical problems. Hence, this review has discussed the recent advances and updates on various approaches of green synthesis of SNPs, their biomedical applications, and their toxicological effects. This will help researchers and readers to investigate further techniques of synthesis of SNPs and industrial applications.
Top1. Introduction
Nanotechnology is synthesis and application of materials at nanoscale with control over shape and size that affects their properties in physical and biological environment. As compared to larger particles, nanoparticles (NPs) exhibit superior characteristics and bioavailability like optical properties, catalytic properties, antimicrobial properties, magnetic properties, at specific size (1-100 nm), structure, shape, chemical nature and surface area to volume ratio. Therefore, since few years, research has been more focused towards the synthesis of various kinds of nanoparticles (NPs) owing to their applications in various fields using different metals, biological molecules, capping agents, drugs molecules, etc. (Rafique et al., 2017). Among the most widely exploited NPs, metal based NPs are very common viz. zinc oxide (Cao et al., 2019; Deekala et al., 2019), cadmium sulphide (Solanki and Rajaram, 2017), gold (Suchomel et al., 2018), silver (Gondil et al., 2019), aluminium (Krause et al., 2020), copper (Kamikoriyama et al., 2019), iron (Saif et al., 2016), nickel (Ahghari et al., 2020), etc. However, noble metals like silver and gold exhibit superior characteristics due to their electrical properties, optical properties and thermal conductivity (Radzuan et al., 2017). Hence, there is a growing interest among the researchers for the synthesis of silver nanoparticles (SNPs) as they have wide range of applications like biological sensors, bio-imaging (Tan et al., 2020), antimicrobials (Yin et al., 2020), microbial contamination control (Simbine et al., 2019), energy generation (Huff et al., 2020), and other biomedical applications (Hussein and Abdullah, 2020).
Therefore, various methods for the synthesis of silver nanoparticles have been reported, including, ball milling (Yadav et al., 2012), pulse laser ablation (Machmudah et al., 2012), evaporation-condensation (Harra et al., 2012), tube furnace synthesis (Baby and Sundara, 2013), etc. However, these methods suffer from several lacunae like non-ecofriendly, more space requirement, surface structure defects, requirement of high temperature, costly equipments, poor-bio-compatability, toxicity, etc. (Iravani et al., 2014), which limits their biological applications. There are various reducing agents including ascorbic acid (Malassis et al., 2016), sodium borohydride (Vu et al., 2018), sodium citrate (Quintero-Quiroz et al., 2019), polyethylene glycol (Fleitas-Salazar et al., 2017), etc. have been reported in the literature. However, considering the toxic effect of these chemicals on the environment and generation of by-products, the researchers shifted their interest towards green synthesis of SNPs by exploiting eco-friendly and biological materials for chemical reduction. Hence, currently efforts are being made for the green synthesis of NPs using biological materials viz. microorganisms, plant extracts, virus DNA, enzymes, etc. (Rafique et al., 2017).
Apart from being eco-friendly, green synthesis of nanoparticles offers other benefits including easy scale up, economical, high reaction rate, less energy-dependent and no requirement of harsh chemicals (Ahmad et al., 2019). Keeping in view the advantages of green synthesis of silver nanoparticles along with their applications as antimicrobials and antioxidant agents, the present review explores the recent advances in the biosynthesis of silver nanoparticles (SNPs) and their bio-medical applications.