How use OnApplicaitonPause() in Android?

When I re-enter after exit with home button in Android, the effects like fire and smoke disappear. Can someone explain me how to use the function “OnApplicaitonPause()” to pause the game and avoid that the effects disappear?
I use both c# and java.

When i re-enter after exit with home button the particles emitter disappear, also if I change the levels. I have to quit the game and restart it.
With “Application.runinBackground = true” works fine with LG P500, but doesn’t work with samsung galaxy next.