When should I use acridine orange/propidium iodide (AO/PI) instead of trypan blue?

Acridine orange/propidium iodide (AO/PI) and trypan blue are two types of stains you can use in viability assays to obtain accurate measurements of the concentration and viability of your samples. 

It’s best to use Acridine orange/propidium iodide (AO/PI) if your samples contain unwanted particles such as red blood cells, tissue debris, or cell debris. 

Trypan blue is the better option if your samples are free from unwanted debris and particles.