Influence of Solution Chemistry on the Deposition and Detachment Kinetics of a CdTe Quantum Dot Examined Using a Quartz Crystal Microbalance

Recent reports underline the potential environmental and public health risks linked to the nano revolution, yet little is known regarding the environmental fate and impacts of most nanomaterials following release in natural soilsand groundwaters. Quantum dots (GDs) are one example of engineered nanomaterials that have been demonstrated to exhibit cytotoxic effects; hence the fate of this material in aqueous environments is of particular interest. In this study, a quartz crystal microbalance (QCM) was used to examine the interaction of a commercially available carboxyl terminated CdTe GD with a model sand (i.e., silica) surface. The deposition kinetics of the GD onto clean silica coated QCM crystals were measured over a wide range of solution conditions, in the presence of either monovalent (K+) or divalent cations (Ca2+). CID deposition rates onto silica were significantly greater in the presence of calcium versus potassium. Solution pH also influenced GD deposition behavior, with increased deposition observed at a lower pH value. The rate of GD release from the silica surface was also monitored using QCM measurements and found to be comparable to the rate of particle deposition when the monovalent salt was used. In contrast, the rate of QD release was considerably lower than the rate of deposition when particles were deposited in the presence of Ca2+. Physicochemical characterization of the CID suspended in varying electrolytes provided insights into the role of solution chemistry on particle size and electrophoretic mobility (surface charge). Measurements of GD size using dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to interpret the QD deposition behavior in different solution chemistries. Lower particle deposition rates observed at high ionic strengths were attributed to aggregation of the QDs resulting in decreased convective-diffusive transport to the silica surface.