Sprite doesn't appear on call - no errors from compiler - how to set Sprites correctly?

I’ve been working out this problem for a while by battling with errors being thrown at me and asking on forms but I’m yet to solve my issue. What I want to do is when my LoseCollider is triggered my Health sprite will change images.

Health sprite:

51930-screen-shot-2015-08-11-at-83428-pm.png

LoseCollider.cs:

public  Sprite Health1; 
public  Sprite Health2;
	
private int totalHealth = 3;

void setSprite () {
                 gameObject.GetComponent<SpriteRenderer>().sprite = Health2;
                 print("SetSprite Called");
}

void OnTriggerEnter2D (Collider2D trigger) {
		if (totalHealth == 3) {
			setSprite();
			totalHealth --;
		} else {
			levelManager = GameObject.FindObjectOfType<LevelManager>();
			levelManager.LoadLevel("Lose");
		}
	}

You don’t have a BoxCollider2D on your object so OnTriggerEnter2D will never get called.