Resources.Load will search for a directory in Assets/Resources.
If you want to put it to Sprites directory then put it inside Resources (ex. Assets/Resources/Sprites).
Then you can just load it like this:
Sprite myFruit = Resources.Load <Sprite> ("Sprites/Graphics_3");
Also make sure that you’ve set your image type to Sprite in the inspector.
If you want to load multiple sprites, use this:
Sprite[] myFruit = Resources.LoadAll <Sprite> ("Sprites/Graphics_3");
See this for more details.