Green synthesis of the silver nanoparticles mediated by pullulan and 6-carboxypullulan

• Pullulan was oxidized using TEMPO protocol to introduce carboxyl groups.
• Pullulan and carboxylated pullulan were used as reducing and stabilizing agents for AgNPs preparation.
• Oxidized pullulan mediated silver nanoparticles exhibits long term stability.
• Excellent antibacterial activity of pullulan/oxidized pullulan silver nanoparticles was achieved.

Unoxidized and carboxylated pullulan (obtained by pullulan oxidation using TEMPO–sodium hypochlorite–sodium bromide system) have been used as mediators for the silver nanoparticles formation (AgNPs), under environment-friendly conditions: using aqueous solutions, room temperature and notably, by using both mediators as reducing and stabilizing agents. The formation of AgNPs was first screened by measuring the surface plasmon resonance peak in the range of 380–440 nm using UV–vis spectroscopy. The morphology of the synthesized silver nanoparticles was determined by TEM, which indicated that the AgNPs differ on shape and thickness of the polymer shell by varying the silver nitrate concentration, different size and shape of AgNPs was achieved. The presence of elemental silver and the crystalline structure of the AgNPs were confirmed by EDX and XRD analyses. Moreover, the possible functional groups of pullulan (oxidized pullulan) responsible for the reduction and stabilization of AgNPs were evaluated using FT-IR.The results showed that both, pullulan and 6-carboxypullulan could be successfully used as reducing as well as capping agents for the AgNPs synthesis which shows potential antimicrobial activity against Gram positive and Gram negative bacteria.