Synthesis and Characterization of Mn:ZnSe/ZnS/ZnMnS Sandwiched QDs for Multimodal Imaging and Theranostic Applications

In this work, a facile aqueous synthesis method is optimized to produce Mn:ZnSe/ZnS/ZnMnS sandwiched quantum dots (SQDs). In this core–shell co‐doped system, paramagnetic Mn2+ ions are introduced as core and shell dopants to generate Mn phosphorescence and enhance the magnetic resonance imaging signal, respectively. T1 relaxivity of the nanoparticles can be improved and manipulated by raising the shell doping level. Steady state and time‐resolved optical measurements suggest that, after high level shell doping, Mn phosphorescence of the core can be sustained by the sandwiched ZnS shell. Because the SQDs are free of toxic heavy metal compositions, excellent biocompatibility of the prepared nanocrystals is verified by in vitro MTT (3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide) assay. To explore the theranostic applications of SQDs, liposome‐SQD assemblies are prepared and used for ex vivo optical and magnetic resonance imaging. In addition, these engineered SQDs as nanocarrier for gene delivery in therapy of Panc‐1 cancer cells are employed. The therapeutic effects of the nanocrystals formulation are confirmed by gene expression analysis and cell viability assay. Mn:ZnSe/ZnS/ZnMnS sandwiched quantum dots (SQDs) are developed as magnetic resonance imaging/optical dual‐mode imaging probes, which exhibit high particle relaxivity and bright Mn phosphorescence. Biocompatible liposome‐SQDs assemblies are developed as multifunctional theranostic agents for dual‐mode imaging and siRNA delivery for gene therapy of pancreatic cancer cells.