Hello Navid

In my experience, the DAPI stock is maintained at 1mg/mL and one must dilute is accordingly for the sample you are staining. In my hands, a dilution of 1:3000 is sufficient for cultured cells; 1:4000 sufficient for thin tissue sections of liver and 1:1000 for tissue sections larger then 50um in thickness. Though the best way is to titrate the DAPI stock and determine which dilution works best for your samples/system. 

Hope this helps.

the concentration of DAPI stock is 1mg/mL, a dilution of 1:1000 is sufficient for cultured cells. But sometimes not all cells could be stained since DAPI is semi - permeable. To address this problem, the 0.5 % triton-100 was used to treat cultured cells for 10 mins.

Thanking you for your response.