Three-layered silver nanoparticles to trace dissolution and association to a green alga

Abstract

Core-shell silver nanoparticles (NPs) consisting of an inner Ag core and successive layers of Au and Ag (Ag@Au@Ag) were used to measure the simultaneous association of Ag NPs and ionic Ag by the green alga Chlamydomonas (C.) reinhardtii. Dissolution of the inner Ag core was prevented by a gold (Au) layer, while the outer Ag layer was free to dissolve. In short-term experiments, we exposed C. reinhardtii to a range of environmentally realistic Ag concentrations added as AgNO₃ or as NPs. Results provide three lines of evidence for the greater cell-association of NPs compared to dissolved Ag over the concentration range tested, assuming that cell-association comprises both uptake and adsorption. First, the cell-association rate constants (k_uw) for total Ag (Ag_NP+D), NPs (Ag_NP) and Au_NP were similar and 2.2-fold higher than the one from Ag_D exposure, suggesting predominant association of the particles over the dissolved form. Second, model calculations based on Ag fluxes suggested that only 6–33% of algal burden was from Ag_D. Third, the significantly lower Ag_NP/Au ratio measured with the algae after exposure (2.1 ± 0.1) compared to the Ag_NP/Au ratio of the NPs in the media (2.47 ± 0.05) suggests cell-association of NPs depleted in Ag. Core–shell NPs provide an innovative tool to understand NP behavior and to directly delineate Ag accumulation from ion and NPs in aquatic systems.

Keywords:

• Silver
• nanoparticles
• algae
• core-shell
• cell-association

Acknowledgements

Natasha Franklin is acknowledged for manuscript review and comments. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the US Government.

Disclosure statement

The authors declare that there is no conflict of interest regarding the publication of this article.

Additional information

Funding

Funding was provided by the Fonds de Recherche Nature et Technologies du Québec, the US National Science Foundation, the National Research Program of the US Geological Survey, and from the University of South Carolina (Smartstate Center for Environmental Nanoscience and Risk and the ASPIRE grant).