Impact of exopolysaccharides on the stability of silver nanoparticles in water.

The stability of commercial silver nanoparticles (SNPs) in aquatic environment plays a significant role in its toxicity to the environment and to human health. Here, we have studied the impact of bacterial exopolysaccharides (EPS) to the stability of engineered SNPs. When nanoparticles are present in neutral water, the nanoparticles exhibited low zeta potential and are least stable. However, in the presence of EPS (10-250 mg/L), the negative surface charge of nanoparticles increased and therefore the propensity of nanoparticles to aggregate is reduced. In UV-visible spectroscopic analysis a decrease in absorbance at plasmon peak of SNPs (425 nm) was observed till the addition of 50 mg/L of EPS, beyond that a blue shift towards 417 nm was observed. The adsorption of EPS was confirmed by Fourier-transform infrared spectroscopy. The EPS adsorbed SNPs were more stable and exhibited the zeta potential of higher than -30 mV.