Ultrafast Photoinduced CIS/ZnS Quantum Dot-to-Doxorubicin Electron Transfer: Implications for Turn-On Drug-Delivery Sensing

Nano-bio interactions play a major role in biomedical applications, particularly in drug delivery, and understanding these interactions is key to the design of efficient and targeted nanocarriers. The key advantage of using such QDs as a delivery vehicle is that drug binding is marked by PL quenching of the QDs, while drug release is indicated by the restoration of PL of the QDs. Investigating the dynamics of the quenching process and understanding the mechanism are of utmost importance in this context. With this background, the interaction between ZnS-shelled copper indium sulfide quantum dots (CIS/ZnS QDs) and a chemotherapeutic drug, doxorubicin (DOX), has been probed using transient absorption spectroscopy. The spectroscopic results, with support from cyclic voltammetry, are consistent with photoinduced electron transfer (PET) being the dominant quenching mechanism from the QDs to DOX. While the process is intrinsically ultrafast, it becomes slower in the presence of bovine serum albumin (BSA), which forms a protein corona on the QDs, as confirmed by fluorescence correlation spectroscopy (FCS).