ABSTRACT
This chemical toolkit has been nicely complemented by GFP (green fluorescent protein) and other visible fluorescent proteins that can be fused by simple cloning techniques selectively to the protein of interest and develop fluorescence without additional cofactors (Tsien 1998; Chapter 3). In this way, proteins can be labeled selectively, as opposed to classical dye labeling techniques. By exploiting physical phenomena such as Förster resonance energy transfer, it is even possible to test whether molecules are in close vicinity (< 10 nm) to each other, thereby closing the gap between the limited optical resolution and molecular dimensions. Moreover, a variety of biological specimens exhibit autofluorescence when they are irradiated. Autofluorescence can provide additional information about the sample, which in contrast to some expensive fluorescent probes, is available free of charge to the researcher.
