Optical imaging of intracellular reactive oxygen species for the assessment of the cytotoxicity of nanoparticles.

The generation of intracellular reactive oxygen species (ROS) was optically monitored using ROS-sensitive gold nanoprobes in response to an exposure of nanoparticles (NPs). Fluorescent dye-labeled hyaluronic acid was grafted onto the surface of gold nanoparticles (HF-AuNPs) for imaging intracellular ROS. The ultrasensitive detection of intracellular ROS was utilized as a powerful analytical tool to assess early cellular toxicities of monodisperse polystyrene (PS) particles with different sizes and different functional groups on the surface. The effect of PEGylation on the surface of PS NPs was also investigated by evaluating intracellular ROS generation. For various PS NPs, the extent of intracellular ROS was well correlated with cellular uptake, apoptosis inducing activity, and cytotoxic effect of NPs. In addition to the nanoparticles, commonly used polymeric gene carriers such as linear and branched polyethylenimine (PEI) were tested to analyze their extent of intracellular ROS generation related to cellular toxicity. This study demonstrated that sensitive and optical detection of intracellular ROS generation can provide a valuable toxicity index value for a wide range of NPs as an early indicator for cellular responses.