## 3 Results and Discussion
### SEM-EDX and HR-TEM Analysis  
SEM-EDX analysis was carried out to reveal the formation of biosynthesized AgNPs by the cell biomass of _L. plantarum_ TA4. Figure 6b shows the formation of particles outside the cell (indicated by the yellow arrow) compared to the control (Figure 6a). From the result, the formation of AgNPs occurred on the cell membrane of _L. plantarum_ TA4. However, only a few particles are observed in Figure 6b which may be due to the effect of sample processing resulting in some particles washed away. From our previous study, we suggested that the functional groups and protein present on the cell membrane of _L. plantarum_ TA4 facilitated the formation of NPs by serving as a binding site for metal ion before the development of NPs [10]. In our current study, a similar finding was reported, and this validated that the formation of metal NPs by _L. plantarum_ TA4 cell was through the involvement of cell membrane. A similar observation was reported by [PERSON] et al. [46] employing _L. reuteri_ in the biosynthesis of selenium NPs, which took place on the cell membrane. Additionally, they also reported that the formation of NPs was initiated by the exopolymeric substance (EPS) secreted by the bacteria. In this study, the extracellular formation of AgNPs was confirmed by EDX spectra, which revealed an elemental silver peak implying the presence of AgNPs (Figure 6c). Moreover, the observed other element peak signals by EDX spectra is due to the chemical used for sample processing and coating process with gold film. Overall, our findings suggested that the formation of AgNPs was facilitated by \begin{table}
\begin{tabular}{c c c} \hline \multicolumn{2}{c}{**Spectra Band (cm–1)**} & \multicolumn{2}{c}{**Functional Group and Vibrational Assignment**} \\ \hline _L. plantarum_ **TA4** & **Biosynthesized AgNPs** & \\ \hline
3254 & 3197 & Hydroxyl group (-OH)/amide group (N–H stretching vibration) \\  & 2924 & C–H stretching vibration \\
1636 & 1634 & Amide I (C=O stretching vibration) \\
1151 & 1518 & Amide II \\
1456 & 1450 & C–H bending vibration \\
1224 & 1209 & C–N stretching vibration, PO2- asymmetric stretching \\
1078 & 1030 & C–O stretching vibration \\
994 & 961 & C–C bending vibration \\ \hline \end{tabular}
\end{table} 
Table 2: Main spectra bands and functional groups interpretation of _L. plantarum_ TA4 and biosynthesized AgNPs. Figure 5: FTIR spectrum of the _L. plantarum_ TA4 biomass (blue line) and the biosynthesized AgNPs (black line). the functional group present on the cell membrane of _L. plantarum_ TA4, which also corresponded to our FTIR results and other studies [35; 46; 47]. HR-TEM was performed to investigate the morphology and size distribution of biosynthesized AgNPs. Figure 6e,\(f\) indicate that the particles are predominantly spherical with an average particle size distribution ranging from 4.7 to 24.3 nm (Figure 6d), with an average size of \(14.0\pm 4.7\) nm. Moreover, the biosynthesized AgNPs were well dispersed without significant agglomeration. The average size obtained by TEM contradicted with the average size obtained using the DLS analysis, whereby a bigger size of AgNPs was documented in the latter. Our DLS result showed that the average hydrodynamic size was approximately 70% (74 nm) higher than the size obtained using TEM. The difference in size obtained between DLS and TEM may be due to several factors. Technically, the DLS measurement analysis is mainly based upon the intensity of light scattered by NPs in the solutions. In this context, the average size obtained is the intensity-weighted mean diameter from the cumulants analysis, in which larger NPs may be weighted significantly compared to smaller NPs [48]. Furthermore, our FTIR results detected the presence of protein and other functional groups from strain TA4 on the surfaces of AgNPs. In this sense,  
Figure 6: Scanning electron microscope (SEM) micrograph of _L. plantarum_ TA4 (**a**) unexposed to Ag\({}^{+}\) (**b**) exposed to Ag\({}^{+}\).