Ultrasmall Near-Infrared Ag2Se Quantum Dots with Tunable Fluorescence for in Vivo Imaging

A strategy is presented that involes coupling Na2SeO3 reduction with the binding of silver ions and alanine in a quasi-biosystem to obtain ultrasmall, near-infrared Ag2Se quantum dots (QDs) with tunable fluorescence at 90 degrees C in aqueous solution. This strategy avoids high temperatures, high pressures, and organic solvents so that water-dispersible sub-3 nm Ag2Se QDs can be directly obtained. The photoluminescence of the Ag2Se QDs was size-dependent over a wavelength range from 700 to 820 nm, corresponding to sizes from 1.5 +/- 0.4 to 2.4 +/- 0.5 nm, with good monodispersity. The Ag2Se QDs are less cytotoxic than other nanomaterials used for similar applications. Furthermore, the NIR fluorescence of the Ag2Se QDs could penetrate through the abdominal cavity of a living nude mouse and could be detected on its back side, demonstrating the potential applications of these less toxic NIR Ag2Se QDs in bioimaging.