Endophytic Fungus Colletotrichum siamense Derived Silver Nanoparticles: Biomimetic Synthesis, Process Optimization and Their Biomedical Applications

The present study validates the biomimetic synthesis of silver nanoparticles using an endophytic fungus, Colletotrichum siamense Prihast (Colleto-AgNPs) derived from Annona muricata leaves. The study also investigates the impact of various process variables, including reductant concentration, the ratio of AgNO₃ to reductant concentration, reaction time, and reaction pH, on achieving optimal efficiency using a factorial design approach (Box Behnken Design experiment). The presence of nanoparticles was verified by observing absorption peaks in the 400–500 nm range. The TEM and SEM-EDX analysis reveals the presence of spherical form nanoparticles. In XRD, a strong peak at 38.10⁰ diffraction indicated that the formed silver crystal was perpendicular to the plane. The average particle size was recorded as 98.48 nm, and the polydispersity index was 0.198 with a zeta potential of -4.92 mV. The toxicity of synthesized Colleto-AgNPs was assessed using brine shrimp lethality bioassay (LC₅₀ of 312.51 ± 32.54 µg/mL). The minimum inhibitory concentration (MIC) of Colleto-AgNPs was determined and reported to be highly effective in suppressing Escherichia coli, Listeria monocytogenes, Staphylococcus aureus, and Salmonella typhimurium. In the agar well diffusion method, Colleto-AgNPs showed strong inhibitory effect against L. monocytogenes (23.98 mm), S. aureus (22.9 mm), E. coli (20.23 mm), and S. typhimurium (17.76 mm) at lower concentrations. Colleto-AgNPs exhibited a significant inhibitory effect against the α-amylase (IC₅₀ of 30.57 ± 0.17 µg/mL) and α-glucosidase (IC₅₀ of 32.30 ± 1.23 µg/mL) enzymes and DPPH radical (IC₅₀ of 26.98 ± 0.30 µg/mL). By conceding this, further investigation can be conducted on Colleto-AgNPs for pre-clinical trials, which would be advantageous in developing innovative medications without any negative side effects for the betterment of humanity.