Abstract
Fluorescent probes that emit in the near-infrared (NIR, 700–1,300 nm) region are suitable as optical contrast agents for in vivo fluorescence imaging because of low scattering and absorption of the NIR light in tissues. Recently, NIR quantum dots (QDs) have become a new class of fluorescent materials that can be used for in vivo imaging. Compared with traditional organic fluorescent dyes, QDs have several unique advantages such as size- and composition-tunable emission, high brightness, narrow emission bands, large Stokes shifts, and high resistance to photobleaching. In this paper, we report a facile method for the preparation of highly fluorescent, water-soluble glutathione (GSH)-coated NIR QDs for in vivo imaging. GSH-coated NIR QDs (GSH-QDs) were prepared by surface modification of hydrophobic CdSeTe/CdS (core/shell) QDs. The hydrophobic surface of the CdSeTe/CdS QDs was exchanged with GSH in tetrahydrofuran-water. The resulting GSH-QDs were monodisperse particles and stable in PBS (phosphate buffered saline, pH = 7.4). The GSH-QDs (800 nm emission) were highly fluorescent in aqueous solutions (quantum yield = 22% in PBS buffer), and their hydrodynamic diameter was less than 10 nm, which is comparable to the size of proteins. The cellular uptake and viability for the GSH-QDs were examined using HeLa and HEK 293 cells. When the cells were incubated with aqueous solutions of the GSH-QDs (10 nM), the QDs were taken into the cells and distributed in the perinuclear region of both cells. After 12 hrs incubation of 4 nM of GSH-QDs, the viabilities of HeLa and HEK 293 cells were ca. 80 and 50%, respectively. As a biomedical utility of the GSH-QDs, in vivo NIR-fluorescence imaging of a lymph node in a mouse is presented.
Highlights
In living tissues, intrinsic chromophores like hemoglobin and water are the major absorbers of visible and infrared light [1]
We report the preparation and characterization of glutathione (GSH)-coated biocompatible Near infrared (NIR) quantum dots (QDs) with a high quantum yield (22%) and a long-term stability (> 1 month) in neutral aqueous solution
As highly fluorescent hydrophobic NIR QDs, CdSeTe/CdS QDs with a core-shell structure were synthesized by a modified method based on the procedure reported by Bailey et al [22,23]
Summary
Intrinsic chromophores like hemoglobin and water are the major absorbers of visible and infrared light [1]. Near infrared (NIR) light ranging from 700 to 1,300 nm can penetrate into deeper tissues For in vivo fluorescence imaging, NIR fluorophores can be used as optical contrast agents. Traditional fluorescent dyes such as Cy7, oxazine 750, and indocyanine green (ICG) have been used as NIR-fluorescent probes for in vivo imaging [4,5]. Traditional NIR-dyes have several disadvantages for use as fluorescent probes: low solubility in aqueous solution, low quantum yield, and low photostability. ICG, the most widely used NIR-dye only provides a quantum yield of 1.2% [6] in blood. The photostability of ICG is very poor and the fluorescence of ICG in aqueous solution diminishes within several days under room right [7]
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