6-Mercaptopurine-Induced Fluorescence Quenching of Monolayer MoS2 Nanodots: Applications to Glutathione Sensing, Cellular Imaging, and Glutathione-Stimulated Drug Delivery

Molybdenum disulfide (MoS2) nanodots (NDs) with sulfur vacancies have been demonstrated to be suitable to conjugate thiolated molecules. However, thiol-induced fluorescence quenching of MoS2 NDs has been rarely explored. In this study, 6-mercaptopurine (6-MP) serves as an efficient quencher for the fluorescence of monolayer MoS2 (M-MoS2) NDs. 6-MP molecules are chemically adsorbed at the sulfur vacancy sites of the M-MoS2 NDs. The formed complexes trigger the efficient fluorescence quenching of the M-MoS2 NDs due to acceptor-excited photoinduced electron transfer. The presence of glutathione (GSH) efficiently triggers the release of 6-MP from the M-MoS2 NDs, thereby switching on the fluorescence of the M-MoS2 NDs. Thus, the 6-MP-M-MoS2 NDs are implemented as a platform for the sensitive and selective detection of GSH in erythrocytes and live cells. Additionally, thiolated doxorubicin (DOX-SH)-loaded M-MoS2 NDs (DOX-SH/M-MoS2 NDs) serve as GSH-responsive nanocarriers for DOX-SH delivery. In vitro studies reveal that the DOX-SH/M-MoS2 NDs exhibit efficient uptake by HeLa cells and greater cytotoxicity than free DOX-SH and DOX. In vivo study shows that GSH is capable of triggering the release of DOX-SH from M-MoS2 ND-based nanomaterials in mice. It is revealed that the DOX-SH/M-MoS2 NDs can be implemented for simultaneous drug delivery and fluorescence imaging.