Encapsulation of cadmium selenide quantum dots using a self-assembling nanoemulsion (SANE) reduces their in vitro toxicity

Although, nanometer-scale semi-conductor quantum dots (QDs) have attracted widespread interest in medical diagnosis and treatment, many can have intrinsic toxicities, especially those composed of CdSe, associated with their elemental composition. Using our self-assembling nanoemulsion (SANE) formulations which we have previously reported to be composed of non-toxic components, i.e., such as vegetable oil, surfactant and water, we hypothesized that their appropriate utilization would reduce the toxicity of QDs by encapsulating the CdSe QDs in our (SANE) system using a modified phase-inversion temperature (PIT) method. SANE encapsulation of the QDs did not alter their emission wavelength of 600 nm which remained unchanged during the encapsulation process. In contrast, zeta potential of encapsulated QDs was reduced from −30 to −6.59 mV, which we have previously reported to be associated with beneficial properties (increased bioavailability and efficacy) for SANE-encapsulated bioactives such as pharmaceuticals. Relative to the untreated controls, the viability of HeLa cells exposed for 48 h to un-encapsulated CdSe QDs at a concentration of 115 μg/mL was 22.7 ± 1.7% (p < 0.05). In contrast, the percentage of viable HeLa cells following exposure to SANE-encapsulated CdSe QDs at the same concentration was 91.6 ± 3.5% (p < 0.05) or a 307% increase in the number of viable cells (p < 0.05). When the dose of CdSe QDs was increased to 230 μg/mL, the percentage of viable HeLa cells after exposure to the un-encapsulated CdSe QDs was 16.1 ± 1.3% compared to controls (p < 0.05). In contrast, at the same increased concentration (230 μg/mL) of un-encapsulated CdSe QDs, the percentage of viable HeLa cells following exposure to SANE-encapsulated CdSe QDs was 87.9 ± 3.3% relative to controls (p < 0.05) or a 448% increase in the number of viable cells (p < 0.05). Exposure of HeLa cells to a nanoblank, (nanoemulsion without QDs), showed no significant effect on cell viability (97.2 ± 2.5%) compared to control cell culture. In conclusion, application of our SANE technology for encapsulating QDs increased cell viability of cells exposed to CdSe QDs while maintaining the original emission wavelength and therefore may be applied to reduce QD toxicity.