Biosynthesis of silver nanoparticles using cellulase derived from <i>Trichoderma longibrachiatum</i>

Enzyme-mediated synthesis of nanoparticles is a green, sustainable substitute for conventional chemical procedures with low toxicity and energy requirements. This study isolated cellulase-producing fungus, isolated the enzyme produced, synthesized silver nanoparticles and characterized the silver-cellulase nanoparticles. These were with a view to chemically immobilizing cellulase on silver nanoparticles. The soil sample used in this study was collected from an orange peel dumpsite. Fungal strains were isolated and the positive isolates were screened on cellulosic basal medium (CBM). Hydrolysis of cellulose was evident following halozone formation. Cellulase was produced via submerged fermentation and culture conditions were optimized for best cellulase production using one factor at a time approach. The cell free supernatant (CFS) was subjected to 0 - 80% ammonium sulphate precipitation. Native molecular weight of the enzyme was determined using gel filtration chromatography. Silver nanoparticles were then synthesized using the enzyme with its formation monitored by UV-Vis spectrophotometer. Furthermore, the ability of the complex to retain cellulase enzymatic activity was determined. The results showed that the best cellulase-producing isolated fungus was molecularly identified to be Trichoderma longibrachiatum. For an incubation period of 5 days, at 30oC and pH 5.0, the highest amount of cellulase was produced. The preferred nitrogen and carbon sources were ammonium sulphate and orange peel respectively. The production of AgNPs by cellulase was verified by a noticeable color shift from pale yellow to dark brown and a UV-Vis absorption at 330 nm. X-ray diffraction (XRD) patterns had four characteristics peaks typical of silver crystals while scanning electron microscopy (SEM) revealed spherical nanoparticles with a polydisperse size distribution, averaging 107 nm in diameter. FT-IR analysis spectra of both the enzyme and the silver nanoparticles showed similar bands which corresponded to the presence of some functional groups such as free thiol groups, amide and carboxyl groups, which were responsible for the synthesized silver nanoparticles. Notably, the AgNPs retained almost 50% of the original cellulase activity, demonstrating that enzymatic functionality was preserved despite potential conformational changes. These findings underscore the industrial potential of cellulase-silver nanoparticle composites in biocatalysis, biosensing, environmental remediation, and biofuel production.