CHAPTER ONE

INTRODUCTION AND LITERATURE REVIEW

1.0 INTRODUCTION

Nanoscience has been the subject of substantial research in recent years. Nanoscience has been the subject of substantial research in recent years. Nanoscience has been the subject of substantial research in recent years. Nanoscience has been the subject of substantial research in recent years. It has been explored by researchers in various fields of science and technology (Kholoud et al. 2010). The novel properties of NPs have been exploited in a wide range of potential applications such as in medicine, cosmetics, renewable energies, environmental remediation, biomedical devices (Quang Huy, 2013), electronics, optics, organic catalysis, vector control, sensor, etc., have drawn extensive attention to this field of study (Mousavand et al. 2007). Among the metals, silver nanoparticles have shown potential applications in various fields such as the environment, bio-medicine, catalysis, optics and electronics (Rao et al., 2000). Silver nanoparticles are mostly smaller than 100 nm and consist about 20–15,000 silver atoms. In its nanoscale form, silver exhibits unique physicochemical and biological activities. This has made them useful as sensor, vector control, antimicrobial, anticancer, and antiplasmodial agents, catalysts, among others (Elemike et al. 2014; Vinod et al. 2014; Kathiravan et al. 2014; Saraschandra and Sivakumar 2014; Namita and Soam 2014).

Concerted effort has been made to synthesize diverse range of silver nanoparticles varying in size, geometry, and morphology because of their potential applications, particularly in electronics (P. V. Kamat, 2002), electrochemical sensing (L. M. Liz-Marzán, 2006), catalysis (F. Zhang, Y. Pi et al., 2007), and antimicrobial properties (T. Sakai et al., 2006). The size, geometry, dispersion and stability often determine the suitability of the nanoparticles for certain applications. Synthesis may involve physical means such as ultraviolet light, microwaves, photo-reduction, or chemical reduction using hydrazine, ascorbic acid, sodium borohydride, glucose, and organic stabilizers or biological means using plant extract, microorganism or plant sap. Several physical and chemical methods have been used to synthesize and stabilize silver nanoparticles (Senapati et al., 2005, Klaus-Joerger et al., 2001). The most popular chemical approaches, including chemical reduction using a variety of organic and inorganic reducing agents, electrochemical techniques, physicochemical reduction, and radiolysis are widely used for the synthesis of nanoparticles.

Although these means are fast and easy, they are either expensive or toxic particularly the chemical method and may lead to non eco-friendly byproducts thus the need for environmental, nontoxic synthetic protocols for nanoparticles synthesis. In the global efforts to reduce generated hazardous waste, “green” chemistry and chemical processes are progressively integrating with modern development in science and industry (Sharma et al., 2009) leading to the developing interest in biological approaches which are free from the use of toxic chemicals as by products. Biological methods can be used to synthesize nanoparticles without the use of any harsh, toxic and expensive chemical substances. The bioreduction of metal ions by combinations of biomolecules found in the extracts of certain organisms (e.g., enzymes/proteins, yeast, fungi, bacteria and plants) is environmentally benign, yet chemically complex (Ankamwar et al., 2005). It has been elucidated that biomolecules with carbonyl, hydroxyl, and amine functional groups have the potential for metal ion reduction and capping of the newly formed particles during their growth processes (Harekrishna et al., 2009, He et al., 2007). Biomolecules in plants and spices extract are essential oils (terpenes, eugenols, e.t.c.), polyphenols, carbohydrates, e.t.c. and can reduce and stabilize Ag+ to Ag0. It provides advancement over chemical and physical methods as it is cost effective and environment friendly.

1.1 LITERATURE REVIEW

Disease-causing microbes are becoming resistant to drug therapy and therefore poses great public health problem. Many researchers are now engaged in developing new effective antimicrobial reagents with the emergence and increase of microbial organisms resistant to multiple antibiotics, which will increase the cost of health care. Colloidal silver has been known for a long time to possess antimicrobial properties and also to be non-toxic and environmentally friendly. It has been used for years in the medical field for antimicrobial applications such as burn treatment (Parikh et al. 2005; Ulkur et al 2005), elimination of microorganisms on textile fabrics (Jeong et al. 2005; Lee et al. 2007; Yuranova et al. 2003), disinfection in water treatment (Russell and Hugo 1994; Chou et al. 2005), prevention of bacteria colonization on catheters (Samuel and Guggenbichler 2004; Alt et al. 2004; Rupp et al. 2004), etc. It has also been found to prevent HIV from binding to host cells (Sun et al. 2005). The mechanism of the bacterial effect of AgNP as proposed is due to the attachment of AgNPs to the surface of the cell membrane, thus disrupting permeability and respiration functions of the cell (Kevitec et al. 2008). It is also proposed that AgNPs not only interact with the surface of a membrane but can also penetrate inside the bacteria (Morones et al. 2005), but the effects of silver nanoparticles (AgNP) on microorganisms have not been developed fully. Researchers believe that the potential of colloidal silver is just beginning to be discovered (Dorjnamjin et al., 2008).

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