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Abstract:
Important information about live cells' behavior and environment may be gained using a new, easy to make fluorescent gold nanocluster, say scientists in Germany and USA.

Fluorescent Clusters Provide Window into Live Cells

Germany | Posted on August 29th, 2011

Studying the behavior of live cells is vastly important to help us understand how our own cells react to changes in environment or invasion, and also to devise better ways to control and contain hostile microbes. To visualize the cells and their processes, labels of some sort are usually required; many of these are fluorescent and can be tracked using external microscopy. Such labels can be laborious to produce and their stability and biocompatibility are a primary concern. Recent advances in nanotechnology have given rise to a new class of fluorescent labels, fluorescent metal nanoclusters. These tiny clusters of metal are small and highly fluorescent and have particular electronic properties because of their size. Their stability can be severely affected by the choice of ligand that sits on the outside of the cluster.

Now, researchers at Karlsruhe Institute of Technology, Germany and University of Illinois in the USA, led by Professor Ulrich Nienhaus, have developed an easy way to make water-soluble fluorescent gold nanoclusters (Au NCs) stabilized with a ligand called dihydrolipoic acid (DHLA). DHLA has two connection points (bidentate) to the cluster which helps to make the cluster extra stable. These Au NCs are highly stable, have bright near-infrared fluorescence emission, are very small, and very biocompatible, all of which makes them promising as novel fluorescent probes for application in biological research. The fluorescence lifetime of the clusters is approximately twice that of background cell fluorescence, so they could easily be visualized within or around a cell using fluorescence lifetime imaging (FLIM).

But the researchers did not stop there. Keen to show just how promising their ligand-stabilized clusters are, they visualized the internalization of the Au NCs by live HeLa cells using FLIM. This technique not only reveals the uptake of the Au NCs by the cells but also provides information about the changed local environment of the Au NCs on uptake through the cell membrane. Au NCs near the cell membrane have a longer fluorescence lifetime than those actually internalized by the cells.

The scientists anticipate that their fluorescent Au NCs will find wide application in biomedical research, including intracellular drug delivery, ultrasensitive molecular diagnostics, and image-guided therapy.

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