Characterization of optimal laser power density and duration of laser treatment for maximum enhancement in transfection efficiency. Nude mice were injected intradermally with 10 μg/mouse pcDNA3-luc in 50 μl volume and immediately treated with femtosecond laser at various laser power densities and with various laser treatment time durations. Mice were imaged 16 hours after DNA injection using the IVIS Imaging System Series 200. Bioluminescence signals were acquired for 1 minute. Laser was first optimized for laser power density, and then for laser treatment time. Untreated mice were used as control. (A) Bar graph showing relative luciferase activity in mice receiving laser treatment at different laser power densities, while keeping laser treatment time duration constant at 80 sec. (B) Bar graph showing relative luciferase activity in mice receiving laser treatment at different laser treatment time durations, while keeping laser power density at 0.04 GW/cm2.