Improvement of the photostability of thiol-capped CdTe quantum dots in aqueous solutions and in living cells by surface treatment

The surface treatment of thiol-capped CdTe quantum dots (QDs) was carried out with a small amount of sodium borohydride (NaBH4) in aqueous solution at room temperature. The treatment effectively enhanced the photostability of QDs and increased the photoluminescence (PL) efficiency by a factor of two as against the original ones. By measuring the PL trajectories of single QDs with a total internal reflection fluorescence microscope under the same irradiation density of 0.72 mu W mu m(-2) at 532 nm, the photostable lifetimes were determined to be 15.2 +/- 5.9 s for surface-treated QDs, and 5.8 +/- 1.9 s for the original ones, respectively. Both the original and treated QDs could be ingested into human hepatocellular carcinoma cells (QGY) by incubation. The photobleaching of cellular QDs was measured with a confocal microscope. Remarkable enhancement was found for the photostability of the surface-treated QDs in QGY cells, demonstrating its advantage for cellular labelling applications.