Green Synthesis of Metal Nanoparticles for Antimicrobial Activity

*Jerushka S. Moodley, Suresh Babu Naidu Krishna, Karen Pillay and Patrick Govender*

## **Abstract**

The development and extensive spread of multi-drug resistant bacteria are considered as a major public health concern. Failures to control severe infections due to antibiotic resistance have augmented healthcare costs as well as patient morbidity and mortality. Presently, natural product-based therapeutics are gaining significant attention both for their antimicrobial effectiveness and for not persuading drug resistance. Furthermore, recent developments in nanoscience on new drug delivery systems built on nanostructured materials from plants and microbes have emerged which focus on targeted delivery and controlled release of therapeutic agents. This review examines the recent investigations on the biological activities of plant and bacterial biological material for silver nanoparticle (AgNP) synthesis. Also, the underlying mechanism of antimicrobial activities of silver nanoparticles against human pathogens will be discussed. A fact of the biological activities and/or chemical responses of plants is required, not only for the discovery of new therapeutic agents, but because such evidence may be of value in disclosing new sources of already known biologically active compounds.

**Keywords:** antimicrobial resistance, biological activities, drug delivery, green synthesis, health, silver nanoparticles

#### **1. Introduction**

The antimicrobial potential of silver (Ag) and Ag-based solutions has long been established, however, their application was considered obsolete upon the discovery of antibiotics [1, 2]. In recent years, the developing crisis of multi-drug resistant pathogenic infections has led to the resurgence in this metal, however, with the use of nanotechnology to generate its nanoparticle form. For this reason, tremendous efforts have been extended in nanotechnology, particularly in the development of green synthetic strategies for silver nanoparticle (AgNPs) production to facilitate their use in antimicrobial therapeutic applications [3].

The interest in silver nanoparticles (AgNPs) as an alternative to current antibiotics has increased profoundly over the last few years. This is owed to the cumulative incidence of microbial drug-resistant infections and the lack of appropriate treatment thereof [4]. The World Health Organisation report of 2014 highlighted the probability of a post-antibiotic era in which common infections and minor injuries

could potentially result in fatalities [5]. Accordingly, concerted efforts have been extended by global pharmaceuticals to formulate new or improved antibiotics. However, despite high research cost-intensive investment in the last decade or so only two new classes of antibiotics have been introduced into the market [6, 7]. The imperative need for the uncovering of novel antimicrobial scaffolds has led to the resurgence of silver, however, in its nano-particulate form [8].

The antimicrobial activities of AgNPs are well established and currently researchers are striving to develop greener synthetic strategies for their production [1, 9]. The use of nanotechnology for the synthesis of AgNPs from environmentally compatible biomaterials is evolving into an important branch of science and technology [10]. To this end, a variety of biological extracts have been explored for the bottom-up synthesis of AgNPs [11]. However, there is an ongoing search to identify novel capping structures to produce AgNPs with increased bio-efficacies. In this context, this chapter points to highlight the use of plants as an alternative green technology for nanoparticle synthesis and their biomedical applications as potential biofactories for antibacterial, antifungal and anti-cancer agents.
