The advancement in nanoparticulate system has a great impact in many scientific areas. Metallic nanoparticles (NPs) such as silver, gold and copper were found to exhibit antibacterial and other biological activities. The phytochemical constituents (Tannins, flavonoids, terpenoids, saponins and glycosides) present in the plant extracts were used for the green synthesis of NPs of desired size and morphology. Moreover, these active molecules act as reducing and capping agents for the synthe¬sis of NPs, which makes them suitable for biomedical applications. Apart from many approach on synthesis of nanoparticles, green synthesis method becomes more preferable because of its ecofriendly and nontoxic approach. This approach might pave the path for researchers across the globe to explore the potential of different herbs in the synthesis of NPs. This chapter will discuss the synthesis of various metal NPs using plants and their phytochemical constituent's involved during the synthesis. A section devoted to the different applications will be presented.
Top1. Introduction
In recent years, nanotechnology is known as an emerging interdisciplinary field, involving biology, physics, medicine, chemistry and material science. The prefix nano is derived from Greek word nanos meaning “dwarf” that refers to things of one-billionth (10–9) in size. The primary concept of nanotechnology was presented by Richard Feynman in a lecture entitled “There’s plenty of room at the bottom” at the American Institute of Technology in 1959. Unlike large materials, nanoparticles (NPs) have characteristic material (physical, chemical, magnetic, electronic, mechanical, thermal, optical) and biological properties (Schmid, 1992; Daniel, 2004). Decreasing the dimension of particles to the nanoscale regime resulted in pronounced effects on the physical properties that significantly differ from their bulk material and this is due to the large number of surface atoms, large surface energy, spatial confinement and reduced imperfections. NPs are usually 0.1 to 1000 nm in each spatial dimension and therefore NPs are considered as building blocks for the next generation of optoelectronics and electronics devices as well as various chemical and biochemical sensors (Wong and Schwaneberg, 2003; Ramanavicius, 2005). Monodispersed NPs with particular shapes have wide applications in the areas of optics, computation, medical diagnostics, cancer therapy, in- vitro assays, ex-vivo and in-vivo imaging and drug delivery. Therefore, interest on developing monodispersed NPs with different size and shape has been increased in the past decade.
There are different methods for the synthesis of metallic NPs. Physical approaches include evaporation-condensation and laser ablation. Various metal NPs such as silver (Ag), gold (Au), lead sulfide (PbS), cadmium sulfide (CdS), and fullerene (a type of carbon nanostructures) have previously been synthesized using the evaporation-condensation method. It was demonstrated that Ag-NPs could be synthesized via a small ceramic heater with a local heating source. The vapor can cool down at a suitable rapid rate which makes possible the formation of small NPs at relatively high yield (Jung, 2006). NPs could be synthesized by laser ablation method, where laser is used as the heating source. The ablation efficiency and the characteristics of produced NPs depend upon many factors such as the wavelength of the laser, the duration of the laser pulses, duration of the laser influence, the ablation time, the medium and the presence of surfactants etc. (Sylvestre, 2004; Kim, 2005). Other physical methods include spark discharge generation, which consists on vaporizing metals by charging electrodes made of the metal and vaporizing it in the presence of an inert atmosphere gas until the breakdown voltage is reached. The arc (spark) formed across the electrodes then vaporizes into metal, which produces very small amounts of NPs (Weber, 2001).