## 3 Results and Discussion
### Antifungal Tests  
In order to observe the antifungal effects of AA.ext, SD.ext, AA.AgNPs and SD.AgNPs, three fungal strains including _A. niger_, _A. flavus_ and _F. oxysporum_ were cultured on the PDA dishes containing those components. Figure 5 showed that three of these fungi on PDA dishes (control sample) were compacted and spread fully on the surface after 96 h. The proliferation of _A. niger_, _A. flavus_ and _F. oxysporum_ on AA.ext and SD.ext dishes was similar to the control. However, the mycelium zone  
Figure 4: TEM images of AA.AgNPs (**a**) and SD.AgNPs (**b**) with the magnification of their photos in the left corner and the SEM micrographs of AA.AgNPs (**c**) and SD.AgNPs (**d**). was reduced on AA.AgNP20, AA.AgNP40, SD.AgNP20 and SD.AgNP40, which demonstrated the inhibitory ability of two biosynthesized silver nanoparticles. Quantitatively, the mycelium diameters of each fungal strain on various media were followed every 24 h until 96 h when the PDA dishes were full of fungi. In Figure 6a, _A. niger_ created the mycelium circle of 20.7 mm on PDA, 19.8 mm on AA.ext and 20.3 mm on SD.ext after 24 h of inoculation. Three values were equivalent to each other, which indicated that _A. niger_ was not inhibited by neither AA.ext nor SD.ext. After every 24 h, the _A. niger_ circles on each dish were larger, which showed the normal proliferation rate. The _A. niger_ zones on AA.AgNP20 and AA.AgNP40 were 15.5 and 12.5 mm after 24 h of incubation. These values were less than that of PDA dishes. The phenomenon was taken place similarly on SD.AgNP20 and SD.AgNP40, the _A. niger_ diameters were 13.3 and 11.0 mm. These smaller mycelium circles indicated the inhibitory effect of AA.AgNPs and SD.AgNPs against _A. niger_ at the concentration of 20 and 40 ppm. The high concentration could inhibit more highly the fungal growth. However, 20 and 40 ppm were not enough to kill all fungi, just to reduce the proliferation, thus _A. niger_ was slowly spread out until 96 h. Indeed, it was reported that 20 ppm of Mesosilver(r) (Purest Colloids Inc., Westampton, NJ, USA) could only reduce approximately 25% of mycelium growth, while 75 ppm inhibited completely the _A. niger_ growth [44]. In the study of [PERSON] et al., also testing with _A. niger_, 5 ppm was just the minimal inhibition concentration of silver nanoparticles stabilized by Myramistin(r) [45]. So, the antifungal capacity of AA.AgNPs and SD.AgNPs against _A. niger_ could be comparable with the Mesosilver products and others. Figure 6b showed the mycelium diameters of _A. flavus_ on various media. On PDA, AA.ext and SD.ext, _A. flavus_ were spread out to 24.5, 24.1 and 23.8 mm after 24 h of incubation; 44.6, 44.7 and 44.2 mm after 48 h; 65.3, 64.8 and 64.3 mm after 72 h and 89.8, 88.8 and 89.5 mm after 96 h. These results implied that _A. flavus_ were not inhibited by AA.ext and SD.ext extracts and proliferated with the comparable rate to control (PDA). In the case of the presence of AA.AgNP20 and AA.AgNP40, _A. flavus_ growth was slowed down. In fact, the _A. flavus_ diameters on AA.AgNP20 and AA.AgNP40 dishes were 19.5 and 15.5 mm after 24 h, 31.7 and 23.8 mm after 48 h, 48.1 and 39.8 mm after 72 h and 66.6 and 53.4 mm after 96 h. If using the higher silver nanoparticle concentrations, the _A. flavus_ diameter was reduced significantly. Changing to other silver nanoparticles of SD.AgNP20 and SD.AgNP40, the _A. flavus_ diameters on dishes were 19.3 and 15.2 mm after 24 h, 30.3 and 23.3 mm after 48 h, 46.3 and 36.8 mm after 72 h and 65.0 and 52.5 mm after 96 h. So, two kinds of silver nanoparticles all demonstrated high antifungal activity against _A. flavus_. Looking at the antifungal activity of other  
Figure 5: The images of growing zone of _Aspergillus niger, Aspergillus flavus_ and _Fusarium oxysporum_ on various agar dishes including the potato dextrose agar (PDA) dishes (control sample), the PDA dishes containing AA.ext and SD.ext, the PDA dishes containing 20 ppm AA.AgNPs and SD.AgNPs after 96 h of inoculation. silver nanoparticle products against _A.