On death numbers and survival times of single dye molecules

In fluorescence measurements on the single molecule level the photochemical stability of the fluorophore is an important factor. We measured in 102 cases the photodestruction of individual tetramethylrhodamine molecules linked to a 217-bp DNA sequence which was attached to a streptavidin-coated glass surface. The fluorophores were excited by a green HeNe laser at 543.5 nm. For each molecule the survival time (time during which fluorescence can be observed), the fluorescence intensity, and the death number (number of detected photons before decomposition) were registered. On the basis of the analysis of single molecule observations, an exponential distribution of the death numbers and survival times of the 102 molecules was found.