Next generation displays and lighting applications are increasingly using inorganic quantum dots (QDs) embedded in polymer matrices to impart bright and tunable emission properties. The toxicity of some heavy metals present in commercial QDs (e.g. cadmium) has, however, raised concerns about the potential for QDs embedded in polymer matrices to be released during the manufacture, use, and end-of-life phases of the material. One important potential release scenario that polymer composites can experience in the environment is photochemically induced matrix degradation. This process is not well understood at the molecular level. To study this process, the effect of an artificially accelerated weathering process on QD-polymer nanocomposites has been explored by subjecting CdSe and CdSe/ZnS QDs embedded in poly(methyl methacrylate) (PMMA) to UVC irradiation in aqueous media. Significant matrix degradation of QD-PMMA was observed along with measurable mass loss, yellowing of the nanocomposites, and a loss of QD fluorescence. While ICP-MS identified the release of ions, confocal laser scanning microscopy and dark-field hyperspectral imaging were shown to be effective analytical techniques for revealing that QD-containing polymer fragments were also released into aqueous media due to matrix degradation. Viability experiments, which were conducted with Shewanella oneidensis MR-1, showed a statistically significant decrease in bacterial viability when the bacteria were exposed to highly degraded QD-containing polymer fragments. Results from this study highlight the need to quantify not only the extent of nanoparticle release from a polymer nanocomposite but also to determine the form of the released nanoparticles (e.g. ions or polymer fragments).
Bibliographical noteFunding Information:
This work was funded by the Center for Sustainable Nanotechnology under the National Science Foundation Center for Chemical Innovation Grant CHE-1503408. J. T. B. acknowledges support by the University of Minnesota Biotechnology Training Grant Program through the National Institutes of Health Grant 5 T32 GM 8347-24. The authors would like to acknowledge the following individuals for consultation and method development: Erin Pryce for CLSM, Bernard Gaskey for SEM and light microscopy, Ronald Lankone for composite fabrication, and Heredeline Ardona for PL. The authors thank the Department of Geographical and Environmental Engineering, the Integrated Imaging Center, Surface Characterization Facility, and the Tovar Lab at Johns Hopkins University for use of their instrumentation.