Aggregation, Dissolution,
and Stability of Quantum
Dots in Marine Environments: Importance of Extracellular Polymeric
Substances
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Abstract
There is an increasing concern that a considerable fraction
of
engineered nanoparticles (ENs), including quantum dots (QDs), will
eventually find their way into the marine environment and have negative
impacts on plankton. As ENs enter the ocean, they will encounter extracellular
polymeric substances (EPS) from microbial sources before directly
interacting with plankton cells. In this study, EPS harvested from
four phytoplankton species, <i>Amphora</i> sp., <i>Dunaliella tertiolecta</i>, <i>Phaeocystis globosa</i>, and <i>Thalassiosira pseudonana,</i> were examined for
potential interactions with CdSe nonfunctionalized and functionalized
(carboxyl- and amine-) QDs in artificial seawater. Our results show
that EPS do not reduce the solubility of QDs but rather decrease their
stability. The degradation rate of QDs was positively correlated to
the protein composition of EPS (defined by the ratio of protein/carbohydrate).
Two approaches showed significant inhibition to the degradation of
carboxyl-functionalized QDs: (1) the presence of an antioxidant, such
as <i>N</i>-acetyl cysteine, and (2) absence of light. Owing
to the complexity in evaluating integrated effects of QDs intrinsic
properties and the external environmental factors that control the
stability of QDs, conclusions must be based on a careful consideration
of all these factors when attempting to evaluate the bioavailability
of QDs and other ENs in the marine environments