A critical but often overlooked component of silver nanoparticle (AgNPs) suspensions involves their behavior following short- and long-term storage. The current study investigates the integrity of citrate-capped AgNP suspensions, nominally 20 nm in diameter, in a series of distinct storage conditions, based on possible combinations of reasonable decisions researchers make, both nanoparticle-based (AgNP and relative citrate concentration) and environmental-based (solution oxygenation and ambient light or dark). AgNP integrity was determined by monitoring single particle stability, aggregation/agglomeration, and oxidation for 104 d. We demonstrate that AgNP suspensions lose their physical and chemical integrity by two distinct processes, 1. oxidation only (light-independent) and 2. oxidation followed by photo-reduction (light-dependent), after initial dilution from a concentrated (and newly synthesized) AgNP stock solution. Based on optical spectroscopy, the effects of oxidation readily observed while the effects of photo-reduction are less obvious, leading to a greater increase in particle diameter, the formation of new, metallic nanoparticles and the oxidation of the parent citrate capping agent. In general, the overall integrity of citrate-capped AgNP suspensions was best maintained when these solutions are stored at the highest AgNP and citrate concentrations studied in the dark following purging with nitrogen gas. This study outlines an implementable strategy for both assessing and monitoring the overall integrity of AgNP suspensions in an effort to harmonize long-term experiments and inter-laboratory consistency.
Citation: Journal of Nanoparticle Research
Pub Type: Journals
Silver nanoparticles, storage, characterization, citrate capped, oxidation, photochemistry