## 3 Biosynthesis of Core Shell Nanoparticles  
In today's world, the synthetic interest for engineered nanomaterials should ideally be inspired by nature instead of using complicated procedures; biosynthesized nanoparticles have beneficial use in clinical trials and in the design of novel therapeutic strategies. Chemically synthesized NPs may be coated with compounds that are used in the synthesis process that limits their application in clinical studies because even the associated impurities in trace amounts can emanate from these experiments. In contrast, the biosynthesis nanoparticles may not have these restrictions [21; 22; 23; 24]. Biosynthetic methods are cheaper and eco-friendlier than the physicochemical synthesis methods [25; 26]. The synthesis process time, depending on the type of bioresource that is used, varies from a few minutes to a few days. In brief, expeditious, inexpensive, and endowed with greater ease of manipulation are some of the salient features of biosynthesis processes. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No.** & **Core Shell NPs** & **Synthesis Method** & **Synthesis Details (Brief)** & **Ref.** \\ \hline \multirow{4}{*}{1} & \multirow{4}{*}{Fe\({}_{3}\)O\({}_{4}\)@carbon} & Combination of hydrothermal and chemical co & & Ferric chloride hexahydrate and ferrous chloride & \\  & & precipitation & & tetrahydrate upon addition of NH\({}_{4}\)OH. Then a carbon & \\  & & & chemical co & layer was coated on Fe\({}_{3}\)O\({}_{4}\) NPs by using starch as the carbon precursor to protect the Fe\({}_{3}\)O\({}_{4}\) magnetic core & \\  & & & & from oxidation. & \\ \hline \multirow{4}{*}{2} & \multirow{4}{*}{Cu@silica and Ag@Si} & Through evaporation via a high powered & One-step: Silica and Cu were placed in a graphite crucible with a weight ratio of 20:1 with Cu on the bottom. The Ag@Si particles were synthesized with a Si:Ag weight ratio of 10:1 with Ag at the bottom. & \\  & & & & \\ \hline \multirow{4}{*}{3} & \multirow{4}{*}{Gold@Silver} & \multirow{4}{*}{Sodium citrate} & Two-step: 4-mercaptoethanol acid ligand (8 uL, 0.57 mM in 0.25 M NaOH) was added under vortex to the as synthesized citrate stabilized AuNPs solution (1 mL). The contents were incubated for 2 h at room temperature, then hydroquinone (30 uL, 10 mM in H\({}_{2}\)O) and AgNO\({}_{3}\) (30 uL, 10 mM in H\({}_{2}\)O) were added under vigorous stirring for 12 h. & \\  & & & & \\ \hline \multirow{4}{*}{4} & Pd@Pt and Cu@Ag & \multirow{4}{*}{Microwave-assisted} & An EG solution containing (PdCl\({}_{4}\), 100 mM) and PVP & \\  & & & (15 wt \(\%\)) was introduced continuously into the quartz & \\ \cline{1-1}  & & & (195 \(\%\)) was heated to 200 \(\%\) using MW irradiation & \\ \hline \multirow{4}{*}{5} & \multirow{4}{*}{Silica@silver} & \multirow{4}{*}{Electroless reduction} & Silica core synthesized by hydrolysis and condensation of TEDS in an alkaline medium. TEGS (3.6 mL) was added to ammonium hydroxide (11.9 mL) in ethanol (8 mL) solution and stirred for 15 h. & \\ \cline{1-1}  & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Some examples of chemical and physical synthesis for core shell nanoparticles. Each method has their advantages and disadvantage, but in generalm the use of biological resources for nanoparticle synthesis is easier, cost-effective, and generates less pollution and circumvent environmental damage than the physicochemical methods in terms of human health and the environment. Nature has provided countless biological resources [27] with millions of bacteria, fungi, and plants bearing numerous structural types that suitable for specific applications [28; 29; 30; 31; 32]. The synthesized NPs decompose after a certain period of time. However, the stability of NPs generated via the biosynthesis method can be enhanced by changing the physicochemical parameters, such as varying the extract concentration or metal ion source, etc.