Handle a lot of collisions

Hello,

I want to reproduce a game I played when I was a child. (I lost the name so I cant show you)
In this game, we control a mass of "particles" which gravitate arround our cursor and the goal is to get in the back of the enemy's particles to "eat" them (when you eat one, it became your particle).

I dont know how to do this, because we cant put a script with health and stuff like this on a single particle, so I have to use gameobject instead ?
But how to handle a lot of collisions without lagging ?

If someone can help me to start, I thank him a lot !

 

No one know how to do this ? I am a bit lost..