Extracellular oxidoreductase exhibiting aryl alcohol oxidase activity for enzyme-mediated synthesis of silver nanoparticles

Aryl alcohol oxidase (AAO) is a ligninolytic oxidoreductase with promising applications in redox biocatalysis and green synthesis. In this study, an extracellular oxidoreductase exhibiting aryl alcohol oxidase activity was obtained from a soil-derived fungal isolate identified as Fusarium redolens via ITS sequencing. The enzyme was purified through ammonium sulphate precipitation, dialysis, and DEAE–cellulose chromatography, yielding a single ∼69 kDa band on SDS-PAGE. Biochemical characterization using veratryl alcohol as substrate showed optimal activity at pH 6–7 and 50 °C, with Km and Vmax values of 0.3 mM and 0.5 µmol min−1, respectively. Thermodynamic analysis indicated favourable catalytic energetics with low activation energy. The purified putative AAO was further employed for enzyme-mediated synthesis of silver nanoparticles (AgNPs) under mild, reductant-free conditions. UV–visible spectroscopy showed a characteristic surface plasmon resonance at 400–420 nm, confirming Ag+ reduction. SEM analysis revealed aggregated nanoscale particles (20–60 nm), while EDX displayed a dominant silver signal around 3 keV. The study demonstrates the role of a purified fungal AAO-like oxidoreductase in extracellular silver ion reduction and highlights its potential as a sustainable biocatalyst for eco-friendly nanomaterial synthesis.