Cellular interactions of colloidal nanosilver and role of alginate capping in prevention of soluble Ag+ leaching

Biological effects including antimicrobial potencies of nanosilver are well known. Nanosilver particularly, small silver particles having a biopolymer as capping agent have been suggested to be more compatible to cells and biological system. Hypothesis says that a biopolymer, being large in size, could prevent the leaching of Ag⁺ ions, which are the primary cause of AgNPs toxicity. In order to corroborate this, we synthesized colloidal silver solution which was both reduced and capped by alginate solution and Ag⁺ ion release kinetics was performed. Overall, it was noted that mechanical agitation aids in the process of ion release which was maximum within first 30 min. (1.8 ± 1 ppm) whereas, only 0.19 ± 0.6 ppm release was observed in non-shaking conditions, in the same duration. After 30 min, the ion release was negligible, irrespective of agitation. Interestingly, the maximum amount of Ag⁺ ion released was only 5.6 % of total. Further, the colloidal silver was examined for antioxidant activity which was surprisingly higher than the standard ascorbic acid solution. Activity of two key digestive enzymes pepsin and α-amylase was assessed in presence of silver particles in SIF and SSF, respectively. Pepsin was unaffected but α-amylase showed reduced activity with increasing particle concentration (p < 0.05). Next, we examined the biological effects of alginate-capped nanosilver on six bacterial strains that predominantly populate wound sites and a panel of mammalian cells. Response of microbes was both dose- and time-dependent. Among tested, P. mirabilis and K. pneumoniae were able to revive themselves after 24 h. On the other hand, IC₅₀ of the nanosilver on HADSCs, A-431, HaCaT, HEK-293, HeLa, and THP-1 was as low as 13.22, 5.96, 6.289, 12.74, 6.0, 5.6 ppm, respectively. Lastly, through intravenous administration of particles in female BalB/ mice and image analysis, we were able to get an overview of particle safety on mouse organs.