Synthesis and Cell‐Imaging Applications of Glutathione‐Capped CdTe Quantum Dots

Abstract

Quantum dots (QDs) are of great interest to biological applications such as fluorescent biosensors and biolabels. Our study describes a synthesis of glutathione-capped CdTe QDs in aqueous solution that is cost-efficient and convenient compared to the conventional organometallic approaches. The fluorescence of the as-prepared glutathione-capped CdTe QDs was tunable from 500 to 650 nm. Without any postpreparation treatment, the glutathione-capped CdTe QDs achieved quantum yields (QYs) as high as 45 %, comparable to, or even better than, QDs derived from organometallic routes. With an overall size as small as 4 nm, they could gain access to cellular targets and stain fine features such as the cell nucleolus. These QDs were successfully conjugated with biotin for immunostaining and with F3 peptide for delivery to live cells, demonstrating their potentially broad application as biolabels.Fluorescent semiconductor nanoparticles or QDs have been extensively investigated in the past decade, and have been widely used as biolabels in imaging and biodetection.[1] Fluorescence imaging can greatly benefit from the use of QDs, which show brighter fluorescence, less photobleaching, and multiple colors with a single excitation. For biolabeling applications, QDs are commonly capped with trioctylphosphine oxide (TOPO) through organometallic synthesis, followed by phospholipid, [2] silica, [3] or polymer [4] coating to impart watersolubility and biocompatibility. With the multilayer coating, the final size of the QD biolabels would typically be 12-20 nm, which might be too bulky to gain access to cells for in vitro and in vivo imaging. In addition, the large dimensions would dramatically lower the labeling efficiency on specific target sites within the cells. Compared to conventionally used organic dyes, the size of QDs presented a major drawback as it limited the range of applications in biolabeling. To overcome this obstacle, water-soluble QDs with only one layer of capping ligand on the surface have been developed by ligand exchange with thiols [5] or phosphine [6] on TOPO-capped QDs.Both the ligand-addition and ligand-exchange methods were complicated, and even the high-quality QDs derived from organometallic methods have exhibited reductions in QY from 65-85 % in the organic phase to 35-50 % in aqueous solution.[7]Alternatively, thiol-capped QDs could be prepared directly in aqueous solution with thiols as stabilizers, but low QYs of 1-10 % were typically obtained.[8] Although their QYs could be significantly improved by a variety of after-treatments, such as photochemical etching, [8] size-selective precipitation, [9] and long-term illumination, [10] these QDs have a tendency to agglomerate during such treatments. Glutathione is a thiol-containing oligopeptide found in most organisms, and it plays an important role in the detoxification of heavy metals in plant cells. The physiological mechanism of detoxification involves the binding of heavy-metal nanoclusters by glutathione and the formation of a phytochelatin shell, cat...

Determination of particle size distribution of water-soluble CdTe quantum dots by optical spectroscopy

“…This increase in size is typical of colloidal synthesis, regardless of the method used for QD production. 39 Furthermore, the sharp line width (full width at half maximum; FWHM) for both absorption and uorescence spectra were sharp, indicating that this method produced GSH-capped CdTe QDs of narrow size dispersion. 29,30 Such physical parameters are of major importance in determining the electronic and optical features of QDs, as well in choosing their most appropriate application.…”

“…Here, we propose a similar mechanism that uses GSH as a surface ligand, since this ligand has a strong appeal for biological systems applications. 39 Reactions (1) to (4) show the steps to GSH-capped CdTe QD formation.…”

CdTe Quantum Dots and Their Bioconjugate with Human Serum Albumin for Fluorescence Imaging

“…Furthermore, the intracellular CdTe QDs can be imaged by strong fluorescence even after several days. As was demonstrated by Zheng et al [33] glutathione-coppedCdTe QDs were stable in cytoplasm and suitable for cell labeling, tracking, and other bioimaging applications. The conduct study also confirmed utility of pure QDs and QDs connected with human serum album for bioimaging of human carcinoma cells.…”

Synthesis of Glutathione Coated Quantum Dots

“…Na 2 TeO 3 in the case of CdTe QDs) or freshly prepared before using in reaction procedure, e.g. H 2 Te (preparation by adding sulphuric acid dropwise to the aluminium telluride (Al 2 Te 3 ) (Zheng et al 2007a)) or NaHTe (forming by reaction of sodium borohydride (NaBH 4 ) with Te powder (He et al 2006;Zhang et al 2003)) in the case of CdTe QDs. However, NaHTe and H 2 Te are unstable compounds under ambient conditions; therefore the synthesis of CdTe QDs generally has to be performed in inert reaction systems (see Fig.…”