Photobleaching was assessed with a 60-W halogen light continuously shone on antibody-dye conjugates for a period of up to 48 h, with serial imaging and analysis of fluorescence intensity. Overall, the DyLight dyes were more photostable than the Alexa Fluor dyes [Figs. 8(a) and 8(b)]. The time point of eight hours was used as a reference point for evaluation, as this would encompass even the lengthiest of most pancreatico-duodenectomies and other oncologic surgeries. At the 8-h time point, there was no significant difference in the percentage of the original intensity in the 488 () and 550 () groups. Alexa Fluor 488 and DyLight 488 retained 96% and 90% of their original intensity, respectively. Both Alex Fluor 488 and DyLight 488 were significantly brighter than FITC, which retained only 45% of its original intensity ( and 0.002, respectively). The 550 group of dyes was the most photostable, retaining approximately 95% of their original intensity for up to 48 h. With the longer-wavelength dyes, however, there was a significant difference between groups. Alexa Fluor 660 lost all of its fluorescence in 1 h. In contrast, by 8 h, DyLight 650 still had 53% of its original fluorescence (). Similarly, in the 750 group, there was a more rapid decline in the fluorescence intensity of Alexa Fluor 750, and by 8-h, Alexa Fluor 750 had no discernible fluorescence DyLight 755 retained 22% of its original fluorescence intensity at 8 h. Overall, DyLight dyes were more photostable than Alexa Fluor.