Dear Ana, you might have some answers from this thread and take a look at the attached file. Wish these would help. 

Best

https://www.researchgate.net/post/Photoreaction_problems_using_DCFDA_staining_for_ROS_analysis_in_oocytes_and_embryos_by_fluorescence_microscopy

In my experience, I used 10 uM for detectng the ROS in vitro assay, I think the things should be pay attention is shorten the observation the time under the UV light for microscopy 

I have used 2.5-5µM, during 30min at 37ºC and it worked fine. Good luck!

Thank you all for your answers

10 uM worked well for us.

Best

S