Achieving high-resolution of 21 nm for STED nanoscopy assisted by CdSe@ZnS quantum dots

Abstract

Although quantum dots (QDs) show strong photoluminescence and high photostability, they are not widely used as probes for stimulated emission depletion (STED) nanoscopy because the excitation of the doughnut-shaped STED beam always generates background noise (the so-called “halo”) that hampers superresolution microscopy. In this study, we attempted to use commercially available CdSe@ZnS QDs with green emission (QD526) as a probe in STED nanoscopy. A lateral resolution of 21.0 nm for a single QD was obtained when using a 488-nm excitation laser and a 592-nm depletion laser. The high resolution achieved was mainly attributed to the fact that no halo was generated around the STED spots. This was also confirmed through spectral analysis in that no spontaneous fluorescence was detected when the QDs were irradiated by the 592-nm laser. The results indicated that the halo could be avoided effectively in QD-assisted STED nanoscopy by tuning the wavelength of the emission peak of the QDs and the depletion laser. This study provides insights into how to easily avoid the halo in QD-assisted STED nanoscopy and how to improve the nanoscopy resolution.