Synthesis of Cysteine-Functionalized Silver Nanoparticles Using Green Tea Extract with Application for Lipase Immobilization

Abstract

ABSTRACTThe application of cysteine-capped silver nanoparticles synthesized using green tea as the reducing agent to immobilize lipase has been reported in the present work. The reducing property of green tea is due to the presence of polyphenolic compounds in its extract which are not oxidized at ambient atmospheric conditions and hence is a suitable reducing agent for green synthesis of nanoparticles. Cysteine-capped silver nanoparticles were synthesized under alkaline conditions by reducing the silver salt by green tea extract in the presence of cystine. Various parameters such as the cystine concentration, pH, temperature, and amount of reducing agent were standardized and their effect on the synthesis process has been initially evaluated by surface plasmon resonance peak analysis. Furthermore, the synthesized nanoparticles were also characterized using X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy. The particle size analysis revealed the average size of the particles to be around 20 nm. The glutaraldehyde-deactivated amino group on cysteine-capped nanoparticles was used to immobilize lipase on its surface. Both crude and immobilized lipases were checked for activity and protein content under standard assay conditions and their activity was found to be 37.7 and 24.9 U mL−1, respectively. The lipase nanoparticle bioconjugates exhibited a good shelf life of 60 days with a marginal decrease in activity. The bioconjugates showed 15% loss in its initial activity at the end of five reusability cycles. This immobilized reusable system has the potential to be utilized for various applications pertaining to the exploitation of lipase in various industries.