Tuning Ternary Zn_1–<i>x</i>Cd_<i>x</i>Te Quantum Dot Composition: Engineering Electronic States for Light-Activated Superoxide Generation as a Therapeutic against Multidrug-Resistant Bacteria

Quantum-confined states of semiconductor nanocrystals offer unique opportunities for selective light-activated photochemistry and generation of specific reactive oxygen (ROS) and nitrogen (RNS) species. Recently, assessment of different ROS and RNS species identified intracellular light-activated superoxide as the prime candidate for selective nanotherapeutic treatments in countering the threat of multidrug-resistant (MDR) pathogens. Here, we show that by carefully tuning the composition of ternary zinc cadmium telluride (Zn1–xCdxTe) quantum dots (QDs), we can engineer the bandgap, electronic states, and the resultant reduction and oxidation potentials, thereby changing the light-activated superoxide generation by these QDs. Using QDs with low cadmium content as alternative candidates for selective light-activated therapy, we show negligible toxicity of these QDs to mammalian cells while maintaining high treatment efficacy against MDR pathogens. These low nanomolar doses of QDs required for therapeutic intervention contain less cadmium than other environmental factors like consuming tubular potatoes, leafy vegetables, animal meat, or even fresh water, further alleviating concerns of elemental toxicity. These results provide design principles for developing different QDs as selective therapeutics to counter the growing threat of antimicrobial-resistant infections