Sample fabrication

The active element is a bio polymeric film obtained from a liquid solution of deoxyribonucleic acid (DNA) and cetyltrimethyl ammonium (CTMA) doped with 4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) dye. The cationic surfactant CTMA is used to make the DNA soluble in organic solvents and then easily mixable with the DCM dye solution.

The DNA-CTMA complex is prepared by magnetic stirring for 2 hours an aqueous solution of DNA sodium salt (200 mL, 0.5 vol.%, Sigma-Aldrich D1626) and CTMA chloride (200 mL, 25 vol.% in water, Sigma-Aldrich 292737). The DNA-CTMA liquid complex is then precipitated for 5 hours, collected by centrifugation at 9000 rpm and finally dried at 70 °C for 12 hours. The result is a 1 gram spongy solid disc with 2 cm diameter and 2 mm thickness.

The DNA-CTMA complex is disolved (200 mg, 4 vol.%) in ethanol and mixed with 1.4 mL of the DCM dye solution (0.5 vol.% in equal parts of ethanol and chloroform). The resulting blend is magnetically stirred for 5 hours.

The lasing devices are fabricated by manually placing the two grains of sand onto a glass substrate at a distance of 3 mm. A small drop (10 μL) of the dye doped blend is then cast onto the substrate, covering a circular area of about 4 mm diameter, in which the sand grains are included. The sample is then dried with a 60 W lamp for 15 minutes.