Facile Synthesis of High-Quality, Water-Soluble, Near-Infrared-Emitting PbS Quantum Dots

PbS quantum dots (QDs) with strong near-infra-red (NIR) fluorescence have been prepared directly in aqueous solution, by using dihydrohpoic acid (DHLA) as a stabilizer. The photoluminescence (PL) emission maximum could be tuned conveniently over a wide range (from ca. 870 nm to 1010 nm) by manipulating the experimental conditions, such as the Ph/S or DHLA/Pb molar ratios. Under optimized conditions, the maximum PL quantum yield was approximately 10%. These resultant PbS QDs were highly stable when stored in the dark at 4 degrees C. After one month of storage, the PL emission intensity decreased by only about 20%, and no obvious spectral redshift was observed. We scaled up further the synthesis of PbS QDs in the lab, where the concentration of QDs was increased to 8 mm from the usual 1 nM. The experimental results from transmission electron microscopy (TEM) imaging, selected area electron diffraction (SAED), and powder X-ray diffractometry (XRD) analyses indicated that the as-prepared PbS QDs had an extremely small diameter (less than 4 nm) and exhibited a face-centered cubic crystal structure. Such aqueous quantum dots are considered to have tremendous applications in biomedical imaging and the fabrication of nanoscaled devices because of their low toxicity, strong fluorescence, excellent water-solubility, stability, and biological compatibility relative to other highly toxic thiol (3-mercaptopropionic acid) stabilized NIR-emitting QDs (such as CdTe, CdHgTe, HgTe). ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)