γ-Irradiated Chitosan Mediates Enhanced Synthesis and Antimicrobial Properties of Chitosan-Silver (Ag) Nanocomposites

Chitosan (CSN) and its derivatives are being exploited for their potential role in agriculture in mitigating environmental stress factors. The present study was aimed to enhance the synthesis of chitosan (CSN)-based silver nanoparticles (Ag NPs) using gamma-irradiated chitosan (IR-CSN) and to study the antimicrobial activity of IR-CSN-Ag NPs. The chitosan-silver nanocomposites (CSN-Ag NPs) were prepared by employing the green synthesis method using normal chitosan (high molecular weight (MW), NL-CSN) and oligochitosans (low MW, IR-CSN). The latter was derived by irradiation with gamma rays (Co-60) at 100 kGy dose to obtain a lower MW (approximately 25 kDa). NL-CSN and IR-CSN (0.0-2.5% w/v) were amalgamated with different concentrations of silver nitrate (0.0-2.5% w/v) and vice versa. The UV-visible spectra displayed a single peak in the range of 419-423 nm, which is the characteristic surface plasmon resonance (SPR) for Ag NPs. The physicochemical properties were assessed using different methods such as transmission electron microscopy (TEM), Fourier transform infrared (FTIR), zetasizer, elemental (CHNS) analysis, etc. The degree of Ag NP synthesis was more in IR-CSN than NL-CSN. The in vitro disc diffusion assay with IR-CSN-Ag NPs exhibited a significantly higher antimicrobial activity against Escherichia coli. Further evaluation of the antifungal activity of IR-CSN and Ag NPs showed a synergistic effect against chickpea wilt (Fusarium oxysporum f. sp. ciceris). The study has provided a novel approach for the improved synthesis of CSN-Ag nanoparticle composites using gamma-irradiated chitosan. This study also opens up new options for the development and deployment of gamma-irradiated chitosan-silver nanocomposites for the control of phytopathogens in sustainable agriculture.