don't open the package unless you're going to use it very soon. leave the package sealed. NANO2 reacts with oxygen, you don't want that to happen.
if you want to make sure that it's still good, you can do the blood test. put SN in contact with real blood; if the blood changes its color to dark brown, then the SN is still good and working, no matter how many years have passed since you bought it.
no, "blood" from steak or meat cannot be used, as steak doesn't actually have blood in it as some people think (that juice on steak is just water combined with a protein called myogoblin). has to be real blood.
there's also another form of test that I'm aware, it's probably called aquarium test, but I don't like it, as it's more complicated than the blood test; if you're interested you can search "aquarium test" on the forum.