Phase transfer-based synthesis of highly stable, biocompatible and the second near-infrared-emitting silver sulfide quantum dots

Previously reported silver sulfide (Ag2S) quantum dots (QDs) emitting in the second near-infrared window (NIR-II, 1000-1400 nm) showed the capacity of in vitro and in vivo bioimaging. Herein, we reported a facile phase transfer- based synthesis to achieve water-dispersed NIR-II-emitting Ag2S QDs. After undergoing phase transfer of Ag+ ions from water to toluene, and the synthesis of Ag2S in toluene followed by ligand exchange, Ag2S QDs were favorably prepared. A series of characterizations confirmed that the prepared products were monoclinic alpha-Ag2S, showing an average size of 3.7 nm. The Ag2S QDs exhibited the maximum emission located at 1045 nm, high PL stability and low cytotoxicity, indicating the feasibility of Ag2S QDs for effective bioimaging in NIR-II biological window. (C) 2014 Elsevier B.V. All rights reserved.