High efficiency amplified spontaneous emission from a fluorescent anticancer drug–dye complex

Abstract External amplified spontaneous emission (ASE) efficiency around 30% is reported for an optically active molecule, which at the same time shows antitumor activity. The complex is formed by the covalent binding of an anticancer drug, tamoxifen, commonly applied in breast cancer therapy, and nitro-2-1,3-benzoxadiazol-4-yl (NBD) dye, which is frequently used as a biomarker in hydrophobic environments, such as lipid membranes. A laser-like pump threshold around 100 kW/cm 2 was found in solutions of the fluorescent drug diluted in acetone or in oil. Agreement with an ASE spatial propagation model, as well as the lack of optical feedback in the walls of the dilution cuvette confirms that ASE is the physical mechanism that explains the high efficiency observed. The waveguide character and the polarization dependence of ASE are also studied. Highly efficient optical gain in such systems suggests new biophotonic applications.