Synthesis and Surface Functionalization of Water-soluble Quantum Dots

Quantum Dots (QDs) for bio-imaging applications need to be water-stable, exhibit high brightness and physico-chemical stability in order to prevent the leakage of toxic ions. In the present work, the direct synthesis of water-soluble CdSe quantum dots and their surface functionalization were achieved through a micro-wave assisted approach in aqueous phase. Glutathione, an essential tri-peptide, was used to functionalize the QDs as an attempt to develop a non-toxic and biocompatible surface. X-ray diffraction analyses suggested that as-synthesized QDs exhibited an alloy arrangement with an average crystallite size of 3.2 nm. HRTEM measurements suggested a size of around 4 nm for glutathione-functionalized QDs. Stable aqueous suspensions of QDs showed strong visible emission (551nm and 561 nm for bare and glutathione-functionalized QDs) under 460nm excitation. The presence of glutathione in the QDs’s surface was confirmed by FT-IR and NRM spectroscopy measurements. Surface characterization of QDs by using FT-IR indicated that glutathione was chemisorbed onto the surface of the CdSe QDs as carboxylate (vas COO at 1630 cm-1 and vs COO at 1390 cm-1). These water-stable glutathione- functionalized QDs can be considered a very promising nanomaterial for bio-labeling and imaging.