Fig. 62. DNA-FRET lasers. (A) Schematic concept of OFRR FRET lasers using DNA scaffolds. (B) Cy5 D lasing could be accomplished via 1 : 1 (top) and 2 : 1 (bottom) D:A DNA constructs, which resulted in decreased lasing thresholds (2.3 μJ mm⁻² for 2 : 1 vs. 4.2 μJ mm⁻² for 1 : 1 for the emission centered at 720 nm). (C) Lasing emission spectrum of a DNA-based cascade-FRET (Cy3–Cy5-Cy5.5) OFRR laser. (D) Lasing emission (integrated between 720 nm and 760 nm) of the cascade-FRET laser was accomplished with a lasing threshold of 6 μJ mm⁻² pump energy density per pulse. Reproduced with permission from ref. 443 Copyright 2010 National Academy of Sciences.