How can I make this button's interactability be toggled on and off?

In this script, at the bottom, I am trying to make it so that once you gain 8 points, the button can be used to get to the next scene. Can someone please help me fix this script? Here is the script: using UnityEngine; using UnityEngine.UI; using System.Collections; using UnityEngine.SceneManagement;

 public class PlayerController : MonoBehaviour 
 {
 
     public float speed;
     public Text countText;
     public Text winText;
     public Text nextLevel;
     public Text levelName;
     public Button PlayButton;
     public void LoadByIndex(int sceneIndex)
     {
         SceneManager.LoadScene (sceneIndex);
     }
 
 
     private Rigidbody rb;
     private int count;
 
     void Start ()
     {
         rb = GetComponent<Rigidbody> ();
         count = 0;
         SetCountText ();
         winText.text = "";
         nextLevel.text = "";
     }
         
     void FixedUpdate ()
     {
         float moveHorizontal = Input.GetAxis ("Horizontal");
         float moveVertical = Input.GetAxis ("Vertical");
 
         Vector3 movement = new Vector3 (moveHorizontal, 0.0f, moveVertical);
 
         rb.AddForce (movement * speed);
     }
 
     void OnTriggerEnter(Collider other) 
     {
         if (other.gameObject.CompareTag ("Pick Up"))
         {
             other.gameObject.SetActive (false);
             count = count + 1;
             SetCountText ();
         }
 
     }
     void SetCountText ()
     {
         countText.text = "" + count.ToString ();
         if (count >= 8) 
         {
             winText.text = "You win!";
             nextLevel.text = "Next Level";
             PlayButton.GetComponent<PlayButton>().interactable = true;
         } 
         else 
         {
             PlayButton.GetComponent<PlayButton>().interactable = false;
         }
     }
 }