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An alternative fabrication method for dye-doped DNA-surfactant complex films was developed and amplified
spontaneous emission (ASE) and lasing under low energy optical pumping were demonstrated. In this new preparation
technique, thin DNA-cethyltrimethylammonium (CTMA) complex films made by a spin coating method were stained
with a hemicyanine dye by soaking them in acetone solution of the dye for one day. Molar ratio of the dye to DNA base
pair for the final products was estimated to be 0.2, the value was much higher than those achieved via usual mixing
method. ASE threshold value under pumping of a pulsed frequency-doubled YAG laser was about 0.3 mJ/cm2. Laser
emission was also attained under the excitation with two interfering beams forming a dynamic grating of gain
coefficient. Durability test indicated that 70% of their initial performance was maintained after 1 hour of continuous
pumping. The technique was applied to water soluble dyes because the DNA complex was insoluble to water as well as
acetone. We employed anionic Eosin Y dye, succeeding in sample formation and ASE emission. Different types of
surfactants were also complexed with DNA, showing variation of emission peak wavelength. These results give a clue
about the structure of the complex or interaction modes between DNA and surfactants, strongly suggesting that dye
molecules are not intercalated into nor bound to DNA double strand directly, but are incorporated in the complex system
via ion-exchange process or aggregating with cationic surfactants.
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