Tracking bio-molecules in live cells using quantum dots

Single particle tracking (SPT) techniques were developed to explore bio-molecules dynamics in live cells at single molecule sensitivity and nanometer spatial resolution. Recent developments in quantum dots (Qdots) surface coating and bio-conjugation schemes have made them most suitable probes for live cell applications. Here we review recent advancements in using quantum dots as SPT probes for live cell experiments.

Beyond the diffraction-limit biological imaging by saturated excitation microscopy

We demonstrate high-resolution fluorescence imaging in biological samples by saturated excitation (SAX) microscopy. In this technique, we saturate the population of fluorescence molecules at the excited state with high excitation intensity to induce strong nonlinear fluorescence responses in the center of laser focus, which contributes the improvement of the spatial resolution in three dimensions. Using SAX microscopy, we observed stained microtubules in HeLa cells with improved spatial resolution. We also measured the relation of the fluorescence and excitation intensity with several kinds of fluorescence dyes and, in the results, confirmed that SAX microscopy has the potential to observe any kind of fluorescence samples in current usage.

Multicolor far-field fluorescence nanoscopy through isolated detection of distinct molecular species

By combining the photoswitching and localization of individual fluorophores with spectroscopy on the single molecule level, we demonstrate simultaneous multicolor imaging with low crosstalk and down to 15 nm spatial resolution using only two detection color channels. The applicability of the method to biological specimens is demonstrated on mammalian cells. The combination of far-field fluorescence nanoscopy with the recording of a single switchable molecular species at a time opens up a new class of functional imaging techniques.