Synthesis and Characterization of Near-Infrared Cu−In−Se/ZnS Core/Shell Quantum Dots for In vivo Imaging

Near-infrared (NIR) semiconductor quantum dots (QDs) represent promising fluorescent probes for biological and biomedical imaging. CuInSe₂ is a good candidate for these applications due to its bandgap in the near-infrared and the reduced toxicity of its components compared to other NIR QD materials (CdTe, CdHgTe, PbS, etc.). Here we present a simple one-pot synthetic route without injection to make fluorescent sphalerite Cu−In−Se core and Cu−In−Se/ZnS core/shell QDs. We show that the photoluminescence (PL) of the resulting core QDs can be tuned from ∼700 nm to ∼1 μm depending on the QD size (from ∼2 to ∼5 nm in diameter). The optical and structural properties of these QDs are consistent with charge recombination via donor−acceptor levels instead of direct excitonic recombination. Finally, we show that the growth of a ZnS shell around these QDs increases their PL quantum yield substantially (up to 40−50% at 800 nm) and allows preservation of their PL properties after solubilization into water and in vivo, as demonstrated by detection of the regional lymph node in a mouse.