Penicillium oxalicum (DS-2) and Fusarium hainanense (DW-8) were isolated from soil and water sample, respectively, collected from the sea coast of Diu, India (20°42'17.3" N 70°54'55.8" E), and were subjected to AgNPs biosynthesis (Fig. 1). The CFF of Penicillium oxalicum (DS-2), Fusarium hainanense (DW-8) and their consortium (DSW-28) was reacted with 10 mM AgNO3 solution in a 9:1 (v/v) ratio. The addition of AgNO3 to the CFF of Penicillium oxalicum (DS-2), Fusarium hainanense (DW-8) and their consortium (DSW-28) resulted in an immediate change in solution color from colorless to light yellow, followed by a change to light brown at 12 h and a dark brown solution at 36 h as the reaction progressed, as shown in Figure 2.
UV-Visible spectroscopic analysis
A UV–Visible spectrophotometer was used to monitor the continuous formation of AgNPs. The synthesized CFF reduced AgNPs that had shown a unique absorption peak attributing to their surface plasmon resonance [13]. The absorption peak for DS-2, DW-8, and DSW-28 in the UV–visible spectrum of an aqueous medium containing silver nanoparticles was with 438, 441, and 437 nm, respectively. With the increasing incubation time, the intensity of the absorption peaks was increased. Even after 72 hours of incubation, there has been no change in the location of the absorption peak (Table 1), indicating that the AgNPs have a uniform particle shape [14]. Furthermore, it is proven that the synthesis of highly dense nanoparticles is responsible for enhancing the intensity of absorption peaks [15]. The results have been found to be consistent with the findings of many other researchers around the world. Figure 3 indicates that the SPR of synthesized AgNPs has not shown any change after 6 months (stored at room temperature).
Band gap energy by Tauc’s plot
A semiconductor's band gap energy describes the amount of energy required to excite an electron from the valence band to the conduction band. The Tauc’s plot proposed using optical absorption spectra was to estimate the band gap energy of amorphous semiconductors in 1966 [16]. The band gap energy (Eg) of all the three synthesized AgNPs was then estimated by extrapolating linear section of the curve (UV-Visible spectra) from Tauc's plot. The AgNPs of DS-2, DW-8, and DSW-28 achieved band gap energies of 2.21, 2.24, and 2.21 eV, respectively, in Figure 4. As a semi-conductive material, these particles with enormous band gap energies can be employed in advanced optoelectronic devices, batteries, and sensors. The band gap value is quite comparable to what has previously been reported in the literature, and it is possible that this value is attributable to the quantum confinement effect [4, 17].
Fourier-transform infrared spectroscopic (FTIR) analysis
Figure 5 depicts the FTIR spectrum of synthesized AgNPs, which shows absorption peaks in the 4000 cm-1 to 500 cm-1 range. The absorption bands in the FTIR spectra of DS-2 were found to be 3265 cm-1, 2127 cm-1, 1661 cm-1, and 760 cm-1. Absorption bands observed for DW-8 were at 3298 cm-1, 2135 cm-1, 1662 cm-1, and 745 cm-1, whereas the absorption bands observed for their mixed CFF (DSW-28) were at 3266 cm-1, 2093 cm-1, 1660 cm-1, and 744 cm-1. The FTIR peaks at various location in the region of 4000 cm-1 to 500 cm-1 indicate the presence of capping and stabilizing biomolecules on the nanoparticles' surface. Dr. Friedrich Menges' software SpectraGryph (version 1.2) was used to analyze ATR-FTIR spectra. Table 2 shows the peaks and their corresponding functional groups, which concurred with the research results of several researchers throughout the world.
At optimum conditions, the incorporation of silver salt into CFF solution results in immediate binding of silver ions with the protein and other molecules present in CFF solution with functional groups such as –OH and C=C being captured, resulting in conformational changes in proteins that represent its hydrophobic residues to the aqueous phase, resulting in infiltration of reducing agents from CFF solution and thus providing capping to silver ions with the formation of stable nanoparticles [18, 19]. Assuming the CFF of the marine fungi Penicillium oxalicum and Fusarium hainanense used in this study, it is conceivable that alkyne, sulfurous and phenolic compounds, proteins, alcohol and other water-soluble biomolecules contributed as reducing and stabilizing agents to the silver nanoparticles [5, 20].
X-ray diffraction analysis
Figure 6 depicts the distinct XRD patterns of mycosynthesized AgNPs by DS-2, DW-8 and DSW-28. XRD pattern of DS-2 exhibited diffraction peaks corresponding to [111], [200], [220] and [311] appearing at 2θ representing the value of 37.89°, 44.19°,64.22° and 77.11°, respectively. XRD pattern of DW-8 exhibited diffraction peaks corresponding to [110], [111], [200] and [220] appearing at 2θ representing the value of 33.18°, 37.76°,46.74° and 66.12°, respectively. The XRD pattern of consortium DSW-28 exhibited diffraction peaks corresponding to [110], [111], [200]and [311] appearing at 2θ representing the value of 33.31°, 38.11°, 44.2° and77.6°, respectively. In accordance with COD ID no. 1100136, these peaks represent crystallographic planes of face-centered cubic (fcc) Ag. The Debye-Scherrer formula was used to calculate the mean particle size of AgNPs [21].

Where,
D represents the crystalline size (nm),
Λ indicates the wavelength of X-ray (0.1541 nm),
β specifies the angular line full width at half maximum (FWHM) of the peak (in radians) and
θ displays the Braggs angle (in radians)
As indicated in Table 3, the mean size of the silver nanoparticles was estimated to be from 14.19 ± 3.14 nm, 8.87 ± 2.31 nm, and 5.14 ± 0.99 nm for DS-2, DW-8, and DSW-28, respectively. The nanocrystalline nature of the mycosynthesized NPs is attested by the extensive pattern of the XRD diffraction peaks [7].
Transmission Electron Microscopic (TEM) analysis
As shown in Figure 7, TEM analysis demonstrated the synthesis of nanocrystalline silver particles. AgNPs with a spherical morphology and uniform size of 11.14 ± 2.39 nm, 7.59 ± 1.31 nm, and 5.73 ± 0.4 nm of DS-2, DW-8, and DSW-28, respectively, were observed. Particles of larger sizes were found in the sample in exceptional cases, although in small proportions. The presence of lattice fringes in the TEM images of synthesized AgNPs demonstrated their crystalline structure, with the 'd' spacing values correlating to the X - ray diffraction patterns. Furthermore, the selected area electron diffraction (SAED) pattern exhibited ring patterns with single spots in a ring (Fig. 7) that are consistent with the XRD patterns. Figure 8 shows the TEM-derived size distribution curve. The nanoparticles with the size range of 5.19 to 21.3 nm for DS-2, 3.04 to 13.5 nm for DW-8, and 1.5 to 17.3 nm for DSW-28 were obtained according to TEM analysis. Until now, a larger size range of AgNPs produced employing various fungus and plant extracts has also been described [13, 22, 23].
Antimicrobial activity of AgNPs
The antimicrobial potential of AgNPs was assessed by measuring the inhibition zone diameter and the observations are shown in Table 4 and Table 5. In this study, the highest zone of inhibition had been observed against Gram-positive bacteria compared to the Gram-negative bacteria. The prospect of employing these AgNPs as a broad-spectrum antimicrobial agent was clearly recognized by these results. This experiment is in correspondence with the view of Mistry et al. (2021) [4] that the probable antimicrobial potential of AgNPs is because of their higher surface-to-volume ratio and their crystalline structure [24]. The AgNPs have been found to rupture the cell membrane, resulting in the generation of reactive oxygen species (ROS) that damage the DNA and proteins, followed by the microorganism's destruction [25]. Many previous studies have reported that AgNPs are more hazardous to the Gram-negative bacteria than Gram-positive bacteria since they have a thinner peptidoglycan layer through which AgNPs can infiltrate and disrupt their proteins and DNA, ultimately leading to microbial death. Conversely, higher amount of nanoparticles are required to show antibacterial potency against gram positive bacteria as they contain thicker peptidoglycan layer [26]. As a consequence, AgNPs aren't highly effective against Gram-positive microorganisms. However, AgNPs synthesized by DS-2, DW-8 and DSW-28 showed very effective results against Gram-positive bacteria (Table 4). Fusarium oxysporum is a plant pathogenic fungus known to cause wilt in many ecologically important plants like cumin, banana that leads to yield loss [27, 28]. To overcome this issue, Fusarium oxysporum was treated by AgNPs synthesized from DS-2, DW-8 and DSW-28. Results obtained after incubation period of 72 h has shown intensive antifungal potential of AgNPs. Zone of inhibition of mixed CFF DSW-28 was higher (19 ± 0.32 mm) in comparison of DS-2 (13 ± 0.33 mm), DW-8 (15 ± 0.31 mm), standard fluconazole (12 ± 0.17 mm) and 10 mM AgNO3 solution (11 ± 0.35 mm) (Table 5). In this study interestingly, AgNPs derived from mixed CFF of marine fungi Penicillium oxalicum and Fusarium hainanense were found to be impressively effective against Gram-positive as well as Gram-negative bacteria and plant pathogenic fungal strain in compare of their individual CFF (DS-2 and DW-8). In mixed CFF, presence of various precious biometabolites from both the fungi could be responsible for higher bioactivity towards human as well as plant pathogens. This characteristic of mycosynthesized AgNPs will contribute in the advancement of broad-spectrum antimicrobial activity [5].
Antioxidant capacity of CFF derived AgNPs
DPPH is a stable molecule that can be reduced by admitting hydrogen or electrons, and it has been extensively utilized to assess antioxidant properties of the silver nanoparticles. In this experiment, various concentrations of biosynthesized AgNPs were reacted with DPPH reagent to assess their antioxidative potency. As a result, AgNPs synthesized by marine fungal cell free filtrate DS-2 and DW-8 and their consortium DSW-28 have shown effective antioxidant potential as their radical scavenging ability was increasing with the increment in their concentration. Figure 9 shows the antioxidant activity of the AgNPs. Their IC50 value was calculated in Microsoft excel-2019 which was about 71.33 (µg/mL) for DS-2, 61.30 (µg/mL) for DW-8 and DSW-28 was about 42.56 (µg/mL). Above mentioned results confirmed that the AgNPs synthesized by mixing their CFF have more antioxidative properties than AgNPs synthesized using their individual CFF which were DS-2 and DW-8 as they possess lower IC50.Antioxidative potential of the silver nanoparticles is due to the adsorption of fungal constituents from CFF on the silver nanoparticle [12]. Metal nanoparticles produced by marine fungi exhibit a wide range of biological activities, including antioxidant, antibacterial, and antimalarial properties. Marine fungus like Aspergillus brunneoviolaceus and Cladosporium cladosporioides have recently been found to produce AgNPs with excellent antioxidant activity. The findings significantly support the use of AgNPs as natural antioxidants for health protection against a wide range of oxidative stressors associated with degenerative diseases. This antioxidant validation is essential for synthesized AgNPs before their utilization against experimental models such as mice or against humans [4, 24, 29, 30].
Larvicidal activity of silver nanoparticles
The synthesized AgNPs from DS-2, DW-8 and DSW-28 were exposed against 4th instars larvae of Aedes aegypti and Culex quinquefasciatus at various concentrations (10–100 µg/mL) for 24 h. Amongst all, the AgNPs synthesized from mixed CFF of DS-2 and DW-8 which is DSW-28 had exhibited potent larvicidal activity. Figure 10 depicts the dose response plot of AgNPs against larvae of Aedes aegypti and Culex quinquefasciatus. The maximum mortality rate observed for DSW-28 was 88% and 92% with LC50 values of 35.37 and 13.35 µg/mL against Aedes aegypti and Culex quinquefasciatus, respectively (Fig-10). Distilled water was taken as a control. No mortality of any larvae was observed in control groups. The mortality rate was significantly augmented with an increasing dose-dependent manner where the highest mortality rate was observed with the increasing concentrations of synthesized AgNPs. This difference in lethal concentrations might be due to differences in secondary metabolites present in the fungi. It has been reported that AgNPs are responsible for impeding the process of food consumption development in mosquito young instar resulting in their death. Furthermore, AgNPs can easily penetrate into the exoskeleton of larvae and attach to the sulfur or phosphorus containing biomolecules like proteins, DNA and RNA which leads to the quick denaturation of organelles and enzymes which could be the possible reason for the death of mosquito larvae. Due to the disturbance in proton motive force important for ATP construction and decreased permeability of membrane by AgNPs, cellular functions may not work properly and cell will die [31, 32, 33]. AgNPs synthesized from DSW-28 had shown highest rate of mortality against both the larvae. Reason behind that characteristic of DSW-28 could be synergistic effect of both the fungal metabolites present and attached on the surface of nanoparticles [10].