## 3 Results and Discussion
### Physico-Chemical and Morphological Characterization of Optimized AgNP  
As stated above, AgNP formation was monitored by measuring the SPR in the UV-Vis region. Nanoparticles were characterized in terms of their size distribution by DLS, and their morphology and state of aggregation were evaluated by AFM and TEM analyses. The stability of AgNP solutions was also evaluated through zeta potential analysis. As shown in Figure 4, the biosynthesized AgNP have an SPR peak located between 402 and 406 nm. This wavelength range suggests that the average size of AgNP produced is homogeneous since the peak is narrow. The SPR peak of small nanoparticles appears at lower wavelengths and vice versa [38]. The nanoparticles' shape is influenced by their size and agglomeration. Some AgNP produced have a larger size, scattering more light and producing a broader SPR peak [39]. A calibration curve using different concentrations of dried AgNP was plotted to determine the concentration of the AgNP suspension. Using the equation obtained from linear regression, the mean concentration of the prepared AgNP was determined, and a value of 3.62 mg/mL was found. The carbohydrate and phenolic contents of AgNP were 0.12 \(\pm\) 0.04 mg glucose equivalents/mL and 0.18 \(\pm\) 0.03 mg gallic acid equivalents/mL, respectively. These values are lower compared to the values obtained for the TE used in their synthesis. However, the presence of these biomolecules in the AgNP suspension indicates that they contribute to the biosynthesis as reducing and stabilization agents for the nanoparticles [40; 41; 42].  
DLS was used to determine the mean particle size and PdI of the AgNP suspension, which were found to be 60 \(\pm\) 17 nm and 0.522 \(\pm\) 0.052, respectively. This technique is a simple and fast method used to determine nanoparticle size. It can also be applied to determine the thickness of the capping or stabilizing layer surrounding metallic particles [43]. The small size of these nanoparticles is ideal for penetrating the skin, and their PdI of around 0.5 is reasonable within the criteria defined and indicates their relatively uniform dimensions. The zeta potential value is a measure of the surface charge of the synthesized AgNP, which promotes their stability in the suspension. The negative zeta potential exhibited (\(-42\pm 4\) mV) provides repulsive electrostatic stabilization for the AgNP.  
Figure 4: UV–vis spectrum of biosynthesized AgNP obtained from TE (5 mL) and AgNO\({}_{3}\) (2 mM, 245 mL) at room temperature after 150 min reaction time at pH 11.  
The AFM and TEM analyses used to characterize the shape, size, and distribution of the AgNP confirm that the nanoparticles have, in general, a spherical-like shape (Figure 5). Based on TEM, the estimated nanoparticle size is around 80 nm, while, according to AFM, the median size is 83 nm. According to the literature, the difference in size obtained between DLS and TEM/AFM is common and could be due to a non-homogeneous dispersion of the samples [44]. Also, for AFM and TEM measurements, the AgNP are adhered to a surface, and in DLS, the nanoparticle size is measured in solution. Spherical and oval AgNP (<87 nm) were obtained from biogenic synthesis using a tomato leaf extract [28]. The previously used tomato leaf extract differs from the one used in this work; however, similar size and polydispersity index values were reported.