One of the challenges in developing a framework for characterizing nanoparticle toxicity is that the number of nanoparticles and their superficial derivatives is very large and continues to expand rapidly. Multiple factors such as size, geometry, surface chemistry, nanoscale topology, electromagnetic activity, and aggregation and degradation processes can modify the original nanoparticle and change its behavior significantly. Secondly, the type of environments and organisms these nanoparticles may be subjected to are also numerous and complex. Thirdly, the number of analytical and computational techniques available to the researcher today spans physical, chemical, biomolecular, ecological and ‘-omics’ based approaches. Thus any combination of nanoparticle, model organismal system and analytical technique is a potential route of investigation and can produce important broad empirical information on the impact of nanomaterials on living systems.
This study is an extension of the analytical framework called DIMER, which involves characterizing the dispersion, imbibition, metabolism, elimination and recycle of nanoparticles to study its life cycle of in the environment. Cadmium selenide quantum dots coated with zinc sulfide were chosen as a model nanoparticle. Similarly the cyanobacterium Synechococcus elongatus PCC 7942 were chosen as the model host organism.
This study characterizes the uptake, distribution and fate of both water insoluble and water soluble CdSe/ZnS quantum dots in cyanobacteria. To quantify the toxicological impact of quantum dots on cells, cell growth rate, membrane destabilization, viability and the activity of photosynthetic pigments were characterized. For characterization of uptake and distribution, flow cytometry, laser scanning confocal microscopy and transmission electron microscopy were used. When quantum dots are dispersed into the environment, their imbibition, metabolism, degradation and elimination from cells depends on their surface coating. Consequently, water soluble quantum dots, which are coated with a hydrophilic coating, showed dramatically reduced degradation rates and resulting hazardous effects on the cells even when observed directly in contact with the cells. However, water insoluble quantum dots were immediately toxic to the cells. The observed toxicity was largely indistinguishable from cadmium toxicity, which is a degradation product of the quantum dot. The primary impact observed is that the cadmium destroys the photosynthetic machinery of the cells. Given the central role of cyanobacteria in many aquatic ecosystems, such damage has serious implications to an ecosystem. Additionally, the cadmium toxicity is persistent in the environment. Once contaminated, the growth media continues to inhibit the growth of new cyanobacteria indicating a long-lasting, toxic effect on the environment
