Simultaneous uptake of a Förster transfer dye pair by diatoms: Application in determination of staining density.

The simultaneous uptake of PDMPO and Rhodamine B as two fluorescent dyes forming a Förster transfer pair by the diatom Cyclotella meneghiniana is demonstrated by in vivo-fluorochromation. The incorporation density in the cell walls was high enough for achieving resonant energy transfer between the two dyes as detected by fluorescence and excitation spectroscopy. The mean fluorescence lifetime of the donor is shortened in the presence of the acceptor by a factor of 0.75. By determining the mean lifetime from the fluorescence decay fitted by three eponentials, the efficiency of the energy transfer and the acceptor concentration is calculated assuming a homogenous distribution. For an initial concentration of both dyes of 5μM in the culture medium which is at the saturation limit of incorporation, an acceptor incorporation density of 0.6mM is obtained. In addition to such quantitative determinations, efficient emitting systems based on resonant energy transfer between two laser dyes may be useful in photonic applications of the hybrid biomineral. By achieving stimulated emission, the presence of optical modes in diatom frustules, which may act as photonic resonators due to the refractive index contrast to the environment in combination with the more or less regular pore pattern, may be characterized further.