In Vivo Bioimaging of Silver Nanoparticle Dissolution in the Gut Environment of Zooplankton

Release of silver ions (Ag + ) is often regarded as the major cause for silver nanoparticle (AgNP) toxicity toward aquatic organisms. Nevertheless, differentiating AgNPs and Ag + in a complicated biological matrix and their dissolution remains a bottleneck in our understanding of AgNP behavior in living organisms. Here, we directly visualized and quantified the time-dependent release of Ag + from different sized AgNPs in an in vivo model zooplankton ( Daphnia magna ). A fluorogenic Ag + sensor was used to selectively detect and localize the released Ag + in daphnids. We demonstrated that the ingested AgNPs were dissoluted to Ag +, which was heterogeneously distributed in daphnids with much higher concentration in the anterior gut. At dissolution equilibrium, a total of 8.3–9.7% of ingested AgNPs was released as Ag + for 20 and 60 nm AgNPs. By applying a pH sensor, we further showed that the dissolution of AgNPs was partially related to the heterogeneous distribution of pH in different gut sections of daphnids. Further, Ag + was found to cross the gills and enter the daphnids, which may be a potential pathway leading to AgNP toxicity. Our findings provided fundamental knowledge about the transformation of AgNPs and distribution of Ag + in daphnids.