Chitosan-thiomer stabilized silver nano-composites for antimicrobial and antioxidant applications

The present study involves a microwave assisted, greener synthesis of chitosan thiomer silver nanocomposites via an innocuous thiourea reagent for antimicrobial applications. The as-synthesized chitosan thiomer acts as a stabilizer, emulsifier, capping agent and reducing agent for chitosan silver nano-composite synthesis. The synthesized thiomers and nano-composites were characterized by various spectroscopic and microscopic techniques. The characterization results demonstrated monodispersed spherical silver nanoparticles (AgNPs) with an average size of similar to 3 nm by TEM characterization. The derivatives and composites were screened for antioxidant activity and antimicrobial activity against bacteria [E. coli Gram (-) and S. aureus Gram (+)] and fungus (Candida albicans). The antimicrobial results indicated a highest inhibition zone of 35 mm and lowest MIC value of 3.7 mu g mL(-1) against E. coli with silver composites. Furthermore, the nanocomposites exhibited greater potential in biological applications as compared to the precursor thiomer, which can be attributed to the high effective surface area of the nanoparticles and plenty of -SH groups in the thiomer structure. Thiomers also exhibited distinguished antioxidant properties ranging from 58-82% even at 100 ppm, while cyclic voltammetric studies revealed comparable results at 50 ppm. The results indicated that the content of -SH group played an important role in antioxidant and antimicrobial activity. The synthesized nanocomposites provide a promising potential to explore their use as a cost-effective and green solution for microbial infection.