Bacterial phototoxicity of biomimetic CdTe-GSH quantum dots

Fluorescent semiconductor nanoparticles or quantum dots (QDs) have excellent properties as photosensitizers in photodynamic therapy. This is mainly a consequence of their nanometric size and the generation of light-activated redox species. In previous works, we have reported the low-cost biomimetic synthesis of glutathione (GSH) capped QDs (CdTe-GSH QDs) with high biocompatibility. However, no studies have been performed to determine their phototoxic effect. The aim of this work was to characterize the light-induced toxicity of green (QDs₅₀₀ ) and red (QDs₆₀₀ ) QDs in Escherichia coli, and to study the molecular mechanism involved.

Photodegradation and reduction power of biomimetic QDs was determined to analyse their potential for radical generation. Escherichia coli cells were exposed to photoactivated QDs and viability was evaluated at different times. High toxicity was determined in E. coli cells exposed to photoactivated QDs, particularly QDs₅₀₀ . The molecular mechanism involved in QDs phototoxicity was studied by determining Cd²⁺ -release and intracellular reactive oxygen species (ROS). Cells exposed to photoactivated QDs₅₀₀ presented high levels of ROS. Cells exposed to photoactivated QDs₅₀₀ presented high levels of ROS. Finally, to understand this phenomenon and the importance of oxidative and cadmium-stress in QDs-mediated phototoxicity, experiments were performed in E. coli mutants in ROS and Cd²⁺ response genes. As expected, E. coli mutants in ROS response genes were more sensitive than the wt strain to photoactivated QDs, with a higher effect in green-QDs₅₀₀ . No increase in phototoxicity was observed in cadmium-related mutants.

Obtained results indicate that light exposure increases the toxicity of biomimetic QDs on E. coli cells. The mechanism of bacterial phototoxicity of biomimetic CdTe-GSH QDs is mostly associated with ROS generation.

The results presented establish biomimetic CdTe-GSH QDs as a promising cost-effective alternative against microbial infections, particularly QDs₅₀₀ .