Biosynthesis of Gold and Silver Nanoparticles Using Phytochemical Compounds

Abstract

Gold and silver nanoparticles are nanoparticles that have been widely used in various fields and have shown good benefits. The method of nanoparticle biosynthesis utilizing plant extracts, also known as green synthesis, has become a promising method considering the advantages it has compared to other synthesis methods. This review aims to give an overview of the phytochemical compounds in plants used in the synthesis of gold and silver nanoparticles, the nanoparticle properties produced using plant extracts based on the concentration and structure of phytochemical compounds, and their applications. Phytochemical compounds play an important role as reducing agents and stabilizers in the stages of the synthesis of nanoparticles. Polyphenol compounds, reducing sugars, and proteins are the main phytochemical compounds that are responsible for the synthesis of gold and silver nanoparticles. The concentration of phytochemical compounds affects the physical properties, stability, and activity of nanoparticles. This is important to know to be able to overcome limitations in controlling the physical properties of the nanoparticles produced. Based on structure, the phytochemical compounds that have ortho-substituted hydroxyl result in a smaller size and well-defined shape, which can lead to greater activity and stability. Furthermore, the optimal condition of the biosynthesis process is required to gain a successful reaction that includes setting the metal ion concentration, temperature, reaction time, and pH.

Keywords: gold nanoparticles; green synthesis; phytochemical compounds; silver nanoparticles.

Figure 1

The mechanism of biosynthesis of metal nanoparticles using plant extracts: (i) activation stage, (ii) growth stage, and (iii) termination stage.

Figure 2

Schema of reducing and stabilizing NPs utilizing polyphenols (e.g., the flavonoid quercetin).

Figure 3

Structure of polyphenolic compounds contained in plant extracts. (a,b) Polyphenols with ortho-substituted hydroxyl. (c) Polyphenol without ortho-substituted hydroxyl. Note: red circle is ortho substituted hydroxyl group as preferred complexation sites.