Mitochondria-targeted ratiometric fluorescent nanosensor for simultaneous biosensing and imaging of O₂^•- and pH in live cells

Intracellular pH undertakes critical functions in the formation of a proton gradient and electrochemical potential that drives the adenosine triphosphate synthesis. It is also involved in various metabolic processes occurring in mitochondria, such as the generation of reactive oxygen species, calcium regulation, as well as the triggering of cell proliferation and apoptosis. Meanwhile, the aberrant accumulation of O₂^•- within mitochondria is frequently intertwined with mitochondrial dysfunction and disease development. To disentangle the complicated inter-relationship between pH and O₂^•- in the signal transduction and homeostasis in mitochondria, herein we developed a mitochondria-targeted single fluorescent probe for simultaneous sensing and imaging of pH and O₂^•- in mitochondria. CdSe/ZnS quantum dots encapsulated in silica shell was designed as an inner reference element for providing a built-in correction, as well as employed as a carrier to assemble the responsive elements for O₂^•- and pH, together with mitochondriatargeted molecule. The developed nanosensor demonstrated high accuracy and selectivity for pH and O₂^•- sensing, against other ROS, metal ions, and amino acids. The remarkable analytical performance of the present nanosensor, as well as good biocompatibility, established an accurate and selective approach for real-time imaging and biosensing of O₂^•- and pH in mitochondria of live cells.