*4.3.3 Light color (wavelength)*

*Smart Nanosystems for Biomedicine, Optoelectronics and Catalysis*

*4.2.5 Boiling*

**4.3 Various conditions**

been discussed.

*4.3.1 Dark condition*

*4.3.2 Sun light conditions*

mixture of metallic salt and plant extract is heated to a burner for particular temperature (10–100 °C) for certain period of time until the solution boils. Care must be taken not to overheat the reaction mixture as it comes out of the bottle. After boiling, the mixture of the solution may cool down at room temperature. To confirm that the synthesis of nanoparticles has been completed, the solution is observed to change the color from light green to dark brown. It may be possible to notice a change of color within minutes or it may take hours a day for a change of color depending on the reducing and capping agent involved in the process [18].

The boiling method could be an approach in which the heat is given up to the boiling point in order to transform the liquid sample into a vapor state. Phytochemicals, secondary metabolites as well as metallic salt reactants are activated by boiling. The free electron of the secondary metabolite or phytochemicals reacts with metallic salt and helps to maintain stability. The reaction mixture of metallic salt AgNO3 and plant extract is boiled on a burner or gas in a beaker for 5–10 min, the boiled solution that come out of a beaker, so care must be taken and the beaker is put out of a gas or a burner so that it may not falls out of a beaker. Once the solution boils, allow the mixture solution to cool down to reach room temperature and the color change from light green to dark brown is observed for verification of the synthesized nanoparticles [18].

The general condition that can be used in a laboratory is discussed in the following paragraph. In general, light of different wavelengths activates the enzyme and activated caused the reduction of silver or metal salts to the formation of nanoparticles and by-products. In this section, light-induced nanoparticle systems have

Until going to light condition, it is very important to understand the effect of the dark condition on nanoparticle synthesis. Thus, the reaction mixture (extract + AgNO3) is kept in a dark state. The nanoparticle synthesis reaction could be performed in dark where the conical flask is covered with aluminum foil to confer the darkness. Originally, the drops of AgNO3 (1 mM) 5 ml are continuously applied to the known concentration of leaf extracts of a specific plant (*Passiflora. foetida*) 95 ml in conical flask. Such mixtures are kept at continuous stirring using a magnetic stirrer. The reaction must be conducted under dark conditions as light oxidized metal, resulting in photo-leaching due to its photo-reactivity properties. Some studies have indicated that synergistic antimicrobial activity is not linked to photo-activity. Nevertheless, the dark state of treated nanoparticles was found to be more stable than UV-light-synthesized particles [14, 18]. The [20] analysis is of synergistic bactericidal activity of silver titanium oxide (AgTiO2) nanoparticles in both light and dark conditions. Therefore, the synthesis of nanoparticles using dark

Corresponding to the dark environment, when the reaction mixture (extract +

silver salt) is maintained under sunlight conditions, it may activate certain

could be a convenient method in certain areas of application.

**102**

The light of different colors could produce different sizes and shapes of nanoparticles. Red, green, and blue are the primary colors of light that are used in different conditions in different ratios to create certain light colors. It is noted that silver nanoparticles under different light colors, such as green, blue, red, yellow and orange 15 W, result in silver nanoparticle synthesis where the blue color light of 15 W shows good UV absorption at 400 nm compared to other color lights. Therefore, the size and shape as well as the stability of nanoparticles could be altered by different wavelengths of light. Like the various wavelength of light, we would like to explore the idea of the influence of sound on nanoparticles [18]. **Figure 4** shows the silver nanoparticle synthesis using various methods and conformation by visual change in colors.

#### **Figure 4.**

*Synthesis of silver nanoparticles using various methods/conditions: sun, microwave oven, sonication, autoclave, yellow bulb, white bulb, UV light and dark (from left to right) [18].*
