Versatile scaffold applications based on MoS₂ quantum dots for imaging mitochondrial pH in living cells

Sensitive and accurate detection and imaging of mitochondrial pH have become significant methods in biological and biomedical research to elucidate the biological functions of mitochondria. Herein, a mitochondria-targeted ratiometric fluorescent nanoprobe was developed to image mitochondrial pH in living cells. This nanoprobe was prepared by covalently linking a mitochondria-targeted ligand (triphenylphosphonium, TPP) and a pH recognition fluorescent indicator (rhodamine, RhB) onto the surface of MoS₂ quantum dots (QDs). In this multifunctional fluorescent nanoprobe, MoS₂ QDs serve not only as nanocarrier for the targeting ligand and pH fluorescent indicator, but also as a fluorescent reference for the ratiometric signal. Indeed, the fluorescence intensity of the MoS₂ QDs is highly resistant to increasing proton concentrations, while that of RhB is sensitive to pH. Ratiometric detection of pH was carried out by comparing the pH-sensitive fluorescence of the RhB-based group with the pH-resistant fluorescence of MoS₂ QDs. After uptake in living cells, the nanoprobe could stain mitochondria specifically, and allowed to image and monitor pH in mitochondria in a satisfactory manner.