**3.3 Nanoparticle synthesis**

*Smart Nanosystems for Biomedicine, Optoelectronics and Catalysis*

of nanoparticles.

amount of silver salt.

**3.2 Preparation of AgNO3 solution**

**3.1 Preparation of plant leaf extract**

number of research papers representing other plant parts for nanoformulation, which includes callus, seed, fruit, stem, flower, tendril and root, which we termed as green synthesis because the initial as well as the byproduct after nanoparticle synthesis both are ecofriendly and biodegradable. This greener method of plantderived reducing agent is used to reduce silver ions to form stable zero-valent silver called silver nanoparticles. Likewise, other metallic nanoparticles, such as gold, copper, silver, titanium, etc., are used for synthesis of nanoparticles using plant extract. The basic synthesis of nanoparticles using plant extract and silver salts was discussed in detail in the following paragraphs. Nanoparticle synthesis is a single pot reaction in which the preparation of the plant extract, AgNO3, is performed and these solutions are combined to form silver nanoparticles [14]. Silver salt was usually used in this chapter for analysis along with plant extract for the formulation

In general, the specific amount of the plant sample is determined in grams for the preparation of the extract in solvents, and the extract filtrate is diluted with sterile distilled water. The diluted filtrate is then used as a reducing agent for silver salts to form silver nanoparticles. The general procedure for the preparation of the extract is as follows: first, the 10 g leaf of Passiflora foetida washed with tap water and dried at room temperature. Second, washed dried leaf specimens chopped into small pieces and macerated directly into 75 ml of autoclaved distilled water. Eventually, the mixture is centrifuged at 4000 rpm for 10 min and filtered with the aid of muslin cloth or syringe filters (stored at 4 °C for future use). **Figure 1** shows the step-wise process of preparation of leaf extract by boiling method for the synthesis of silver nanoparticles [18]. As we are dealing with nanoformulation, it is very important to use the (diluted) plant extract at a minimum to reduce the

Similar to plant extract, the amount of silver salt must be low and precise in order to form stable nanoparticles. If the reaction of silver salt is more or more in bulk, the synthesis of nanoparticles may be hindered. For this purpose, the minimum quantity of reacting material is used for the effective, slow, nucleation of nanoparticles. Because silver nitrate (AgNO3) is very expensive, it is important to

*Step-wise process of preparation of leaf extract of* Passiflora foetida *by boiling method for the synthesis of* 

**98**

**Figure 1.**

*silver nanoparticles [18].*

Nanoparticles are easily synthesized by combining the appropriate concentration of plant extract and silver salt, and in short, 1 mM of silver nitrate (95 ml) is mixed with 5 ml of (diluted) leaf extract and kept at constant stirring in the 250 ml round bottom flask on a magnetic stirrer at room temperature. Later, solutions are allowed to react with each other in order to form nanoparticles. Synthesis of silver nanoparticles is confirmed by a change in the color of the solution from light green to dark brown, detected clearly by the naked eye (visual observation). This noticeable change in color is the primary indicator for the synthesis of Ag nanoparticles. The general optimization method for nanoparticle synthesis is shown in diagrammatic form in **Figure 2**.

Unless, after some time, the mixture does not show any change in color, it would be due to the acidity of the medium. It has been found in several papers that the alkaline solution is favorable to nanoparticle synthesis. Thus, 0.1 mM of NaOH is therefore used to produce a mixture solution into alkaline. It is vital that either the silver salt or the extract can be applied gradually using a syringe. The release of a moderate volume of extract into silver salt requires the proper synthesis of silver nanoparticles. The complete process of green synthesized silver nanoparticles at room temperature is shown in a diagrammatic form in **Figure 3**.
