Fig. 1.

Schematic of experimental setup: 2-mm tip of a fiber OFRR (SMF-28^® optical fiber core) in liquid environment (tris-EDTA buffer solution) is pumped with OPO laser source through a confocal setup, and the laser emission is simultaneously collected by a spectrometer. The fiber OFRR supports WGM and its evanescent field interacts with surface-attached molecules, providing a feedback for lasing phenomena. Inset: Single molecular layer of DNA laser gain on the OFRR surface. The fiber OFRR is immersed in a series of solutions and finally functionalized with the probe ssDNA. The fiber DNA probe is hybridized with the target DNA in liquid sample, followed by the intercalating dye staining. The active DNA intercalating dye (SYTO^®-13 Green Fluorescent Nucleic Acid Stain) combined with the hybridized DNA molecules contributes to the laser.