Photocatalytic activity of colloidal CdS nanoparticles with different capping ligands

We report on the synthesis and characterization of cadmiumsulfide quantum dots (CdS-QDs) with three different types of capping ligands, mercaptoacetic acid (CdS-MAA), cysteamine, and 2-mercaptoethanesulfonic acid (CdS-CM), or tiopronin (CdS-TPN). All three types of QDs generate reactive oxygen species (ROS), in particular, superoxide- and hydroxyl radicals, upon irradiation with UV light. The ROS were analyzed using electron paramagnetic resonance (EPR) spectroscopy. Moreover, the hydroxyl radical generation from the three different QDs was monitored using a terephthalate-based fluorimetric assay. The three QDs were then used as photocatalyst to trigger the peroxidase activity of horseradish peroxidase.