Researchers can follow individual molecules by marking these with fluorescent dyes and then following them with a microscope. This method has already provided many new insights. The use of the method in living cells, however, is limited due to the low brightness and limited stability of the fluorescent markers used. Researchers from this programme have therefore developed gold nanorods as alternative markers.
These gold rods are one thousand times brighter than traditional fluorescent markers. For the imaging of the gold rods, use is made of two-photon luminescence. With this the gold rod absorbs two photons as a result of which it enters an excited state. When the electrons in the gold rod fall back to the ground state, they emit light. Using two-photon luminescence, both the resolution and the background intensity of the microscopic images are considerably improved. This makes it possible to follow individual gold rods in living cells over a longer period of time to within an accuracy of one billionth of a metre .
In the past year researchers from this programme have synthesised gold rods and coated them in a chemical layer that prevents them from sticking to each other or to cell components. Chemical compounds that bind to certain proteins have also been attached to the rods. This allows gold rods to be attached to selected proteins .
Now the researchers are focusing on the glucocorticoid receptor protein , which plays an important role in activating genes that are dependent on n hormones. They link the glucocorticoid receptor to both the gold rod and a green-fluorescent protein. The activity of the protein is subsequently studied. With this approach the researchers can compare the characteristics of gold rods with traditional fluorescent markers .
Researchers have demonstrated that the binding of a single protein can be detected using changes in the spectrum of a single gold rod. By capturing the gold rod in an optical trap, this can be brought to a desired environment. Finally the researchers have combined microscopy and spectroscopy so that changes can be rapidly measured in several gold rods at once. Over the next year these techniques will be used to follow individual proteins in living cells .