Pigment mediated biosynthesis of crystalline silver nanostructures: Structural characterization and enhanced multifunctional bioactivity

Harnessing the innate biochemical intelligence of nature is redefining nanotechnology. The present study reports the use of a red pigment from Talaromyces australis for the synthesis of AgNPs using sunlight. Color changes confirmed the formation of AgNPs, which was evidenced by the observation of a SPR peak at ∼ 430 nm. TEM revealed spherical AgNPs with an average size of 16 ± 2 nm, whereas NTA showed a narrow size distribution and excellent colloidal stability. The FCC structure was confirmed using XRD, and FTIR confirmed the involvement of three functional groups (hydroxyl, carbonyl, and C–O) in the reduction and stabilization of AgNPs. Disc diffusion assays indicated that the pigment inhibited the growth of Escherichia coli , Staphylococcus aureus , Salmonella typhi , Pseudomonas aeruginosa , and Bacillus subtilis , and that the inhibition was concentration-dependent (zones: 9.33–15.66 mm). Antimicrobial activity was pronounced at a higher concentration of AgNPs (1 mg/mL), with zones of inhibition between 12.33–13.00 mm. MIC confirmed that antimicrobial activity was enhanced for the AgNPs (500 µg/mL for crude pigment and 62.5 µg/mL for AgNPs). Improvements were also observed in antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay (DPPH IC₅₀ < 10 µg/mL) and 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid assay (ABTS IC₅₀ < 10 µg/mL) and dose-dependent cytotoxicity (GI₅₀ = < 10 µg/mL and TGI = 53.0 µg/mL). These findings imply that Talaromyces australis pigment is a highly efficient and sustainable bio-reductant for the rapid biosynthesis of multifunctional AgNPs with improved biomedical potential. • Fungal pigment enabled green synthesis of stable, crystalline silver nanostructures. • AgNPs exhibited spherical morphology (18–26 nm) with distinct polycrystalline SAED rings. • FTIR confirmed pigment functional groups coordinating and stabilizing AgNPs surfaces. • Pigment-AgNPs showed enhanced antibacterial efficacy with reduced MIC values. • AgNPs displayed strong anticancer activity with GI₅₀ < 10 µg/mL against HeLa cells.