## 3 Biosynthesis of Core Shell Nanoparticles
### Greener Synthesis of Core-Shell Nanoparticles Using Plants  
Plants-mediated synthesis of core-shell nanoparticles is advantageous when compared to processes that are assisted by bacteria and fungi [36]. [PERSON] et al. (2017) [37] reported one-step biosynthesized magnetic nickel/iron-oxide core shell NPs using 20 grams of _Moringa oleifera_ extract. [PERSON] et al. [38] reported one-step biosynthesized gold/silver core shell NPs using _Dioscorea bulifera_. [PERSON] et al. [39] reported two-step biosynthesized Fe\({}_{3}\)O\({}_{4}\)-Ag core/shell NPs (50 nm) using _Vitis vinifera_ stem extract. Au-Ag core shell NPs (10 nm) were synthesized via one-pot method using grape water [40], a herbal medicinal drug. Plants seem to be the ideal candidates as they are suitable for expeditious large-scale green synthesis of core-shell NPs; the rate of synthesis being faster than those observed for processes aided by microorganisms [41]. Various core shell NPs with diverse structures, shapes and sizes have been synthesized using plants and some are documented in Table 2.  
The plant extracts contain chemical entities with numerous functional groups that are involved in the reduction of metal salts and capping of ensuing nanoparticles and therefore, are ideally suited for biological evaluation [50]. Additionally, some effective factors are widely distributed in biological systems and their combined influence have been reported in the biosynthesis of nanoparticles using plants. The individual effect of enzymes, such as nitrate reductase enzyme [51,52], amino acid (Tyrosine) [53], carbohydrate, such as starch and glucose (with 17 months, stability) [54], terpenoids, polyphenols, alkaloids, phenolic acids, flower pollen, and proteins have been implicated in the synthesis of nanoparticles [55]. In plant mediated-synthesis of nanoparticles, the nature of extract has a significant effect on the availability of functional groups such as aldehyde, hydroxyl, carboxyl, amino, etc. on the surface of biosynthesized nanoparticles. Accordingly, the coated functional groups on surface of these nanoparticles can bind to a variety of biological structures, including antibodies, proteins, DNAs, enzymes, polymers, etc. Thus, one of the added advantages of the greener synthesis using the plant extract, in contrast to other synthesis methods, is that the choice of extract not only reduce the metal salts, but also provides certain functional groups on their surface. Importantly, the selection of plant extract is critical for achieving the suitable functionalization of nanoparticles as the avoidance of aggregation of biosynthesized nanoparticles and attaining a suspension of stable nanoparticles is a prerequisite for advancement of research. The functional groups on biomolecules can be divided into three types of hydrophilic (such as ammonium salt, polyol, lysine, an amino acid, citric acid, vitamin), hydrophobic (fatty acids, alkyl phenol), and amphiphilic functional groups (soluble in water and acids, such as lysine). Natural plant-derived polymers are an interesting group of compounds used for coating of NPs (Table 3). These are high molecular weight polymeric compounds that are built-up of small repeated  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**No. ** & **Plant** & **Nanoparticles Type** & **Method for Extract Preparation** & **Size (nm)** & **Ref. ** \\ \hline \multirow{2}{*}{1} & _Moringa_ & \multirow{2}{*}{Ni/Fe\({}_{3}\)O\({}_{4}\)} & 20 g leaves extract at 80 \({}^{\circ}\)C with 100 mL & 16–20 & [37] \\  & _Olefren_ & & of de-ionized water for 2 h. & & \\ \hline \multirow{2}{*}{2} & _Discorrea_ & \multirow{2}{*}{Au/Ag} & 5 g of the dried tubers powder boiled in & 9 nm core total & \\  & _bulifera_ & & 100 mL of distilled water for 5 min. & diameter 15 & [38] \\ \hline \multirow{2}{*}{3} & _Vitis vinifera_ & \multirow{2}{*}{Fe\({}_{3}\)O\({}_{4}\)-Ag} & 10 g stem powder mixed with 100 mL & \multirow{2}{*}{Below 50} & [39] \\  & _Antigonon_ & & distilled water.