Cation Exchange-Based Facile Aqueous Synthesis of Small, Stable, and Nontoxic Near-Infrared Ag2Te/ZnS Core/Shell Quantum Dots Emitting in the Second Biological Window

Facile aqueous synthesis of near-infrared Ag2Te quantum dots (QDs) and Ag2Te/ZnS core/shell QDs emitting in the second biological window is reported. The QD synthesis is based on a straightforward cation exchange process between CdTe QD and Ag+ ions conducted in aqueous solution. The prepared Ag2Te QDs possess near-infrared emission ranging from 900 to 1300 nm and a quantum yield up to 2.1%. A ZnS shell was grown on the Ag2Te QD to further enhance the photoluminescence intensity with a quantum yield of 5.6%. These Ag2Te/ZnS core/shell QDs possess robust colloidal stability and photostability with minimum photoluminescence fluctuation upon incubation for 72 h in biological buffer or continuous laser excitation for 120 min. Also, These QDs possess small hydrodynamic size (similar to 7.6 nm) and are non-cytotoxic to human cells, which is ideal for optical bioimaging in the second biological window.