## 3 Results and Discussion  
### The Formation of Biosynthesis LAGNPs Including AA.AgNPs and SD.AgNPs  
At room temperature, two kinds of silver nanoparticles (AA.AgNPs and SD.AgNPs) were obtained by only one reaction of silver (I) ions with AA.ext and SD.ext. The first observed phenomenon was the color change, the broths had a pale green color and turned to reddish-brown at the stopping point of the reaction. Furthermore, a UV-vis spectrophotometer was utilized to scan two extract solutions and two reacted mixtures containing AA.AgNPs and SD.AgNPs. The UV-vis spectra of AA.ext and SD.ext (Figure 2a,b, dash lines) did not show any peak in the wavelength region of 350-750 nm. Differently, the UV-vis spectra of AA.AgNP and SD.AgNP solution (Figure 2a,b, solid lines) had a peak centered at 433 nm. For both AA.AgNPs and SD.AgNPs, the peak height was increased as a function of reaction time, and was almost saturated after 8 h of reaction. This peak was caused by the absorption of the plasmonic silver nanoparticles, so the formation of AgNPs was confirmed. However, the AA.AgNPs exhibited a broadened peak, while the SD.AgNPs had a sharp one. The surface plasmon resonance of silver nanoparticles depended on the free electrons interacting with the electromagnetic radiation (light) [32]. Thus, the difference in dimension and morphology or silver nanoparticles could affect on the collective excitation oscillations that might lead to the different absorption peaks. Besides, AA.AgNPs and SD.AgNPs were formed from two different extracts containing the variously reducing amounts, which could lead to creating different concentrations of silver nanoparticles. The broadened peak of AA.AgNPs indicated a higher concentration. Considering the reaction mechanism, the phytochemicals of _A. aspera_ and _S. dulcis_ played the role of reducing agents, and the silver (I) ions were the oxidizing ones. Due to the abundant compositions in each extract, it might have a lot of oxidation-reduction reactions taking place. However, the phytoconstituents in each plant have not been completely investigated yet, missing understanding would remain. With an attempt connecting all the reported studies, we could comprehend some reactions in detail. _A. aspera_ was reported to have saponins, gallic acid, quercetin, kaempfer, rutin, etc. [18]. Saponins possess the properties of the surfactant having both a hydrophilic and hydrophobic portion. The hydrophilic part is comprised of glycosides, which can reduce silver (I) ions into AgNPs [33]. Gallic acid possessing three hydroxyl groups on phenyl rings can cleavage the hydrogen ion and give one electron to silver (I) to become an oxidized gallic acid, and silver (I) ions become AgNPs [34]. In the case of quercetin, kaempfer and rutin, they also have the hydroxyl groups of phenyl ring, and can act as an oxidant with a similar mechanism of gallic acid [35; 36; 37; 38]. _S. dulcis_ was found to contain flavonoid, alkaloid and tannin [24] which also possess the hydroxyl groups performing the role of the reductant. Besides, _S. dulcis_ has carbohydrates and glycosides [24], which are well-known as a reductant. On the other hand, these phytoconstituents have a chelating ability with Ag due to containing oxygen of hydroxyl and carboxylic acid groups. It is a beneficial factor to stabilize the biosynthesized silver nanoparticles. Thus, FTIR spectroscopy was performed to explore the functional groups surrounding nanoparticle surfaces. Figure 2c described the FTIR spectra of AA.AgNPs (i) and AA.ext (ii). There was the pointed trough of 3461 cm\({}^{-1}\) assigned to the O-H stretching band. The O-H groups modified on AA.AgNPs exhibited a sharper trough than O-H of phytoconstituents in the AA.ext extract. It could be explained by the H-bonding in AA.AgNPs being weaker than that in the AA.ext extract. The small trough at 2926 cm\({}^{-1}\) and the medium one at 1662 cm\({}^{-1}\), 1384 cm\({}^{-1}\) and 1070 cm\({}^{-1}\) were caused by the C-H stretching, C=O stretching, O-H bending and C-O stretching vibrations.