PIC16F72A ADC Not reading

#pragma config FOSC = XT        // Oscillator Selection bits (XT oscillator)
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)
#pragma config PWRTE = OFF      // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOREN = OFF      // Brown-out Reset Enable bit (BOR disabled)
#pragma config CP = OFF         // Flash Program Memory Code Protection bit (Code protection off)
#include <xc.h>
#include"lcd.h"
#include<stdio.h>

#define _XTAL_FREQ 1600000
unsigned int  adc;


 __interrupt isr()
{
     if(ADIF==1)
        {
         adc = ADRES;
         ADIF = 0;
         GO_DONE = 1;
        
              
        }
}
    
    

void adc_initilize()
{  ADCON0 = 0x81; // 32 Tosc 7 ADC ON
   ADCON1 = 0x05; // all input makes analog input
   ADIE=1; //Enables the ADC interrupt
   ADIF=0; //clear the A/D Converter Interrupt interrupt flag
   __delay_us(40);
    
  
}
     void main(void) 
    {    unsigned char buffer[8];
         OPTION_REG &= 0x7F;
         TRISB =0x00; 
         TRISA=0x01;// for adc first channel as input
         unsigned int i; 
         TRISB =0x00;
         GIE =1;
         PEIE = 1; 
         ADIE = 1;                  // Enable ADC interrupt
         LCD_init();
         adc_initilize();
         LINE1;     
         string("  ADC");
         LINE2;
         //string("Stuck Here1");
         LINE1;
          
        
       while(1)
               { 
                    //  ADCON0 = ADCON0|(0X04); // ADC starting GO/DONE Bit setting
                    GO_DONE = 1;           
                    LINE1;
                    string("ADC Reading");                   
                    LINE2; 
                   sprintf(buffer,"%d",adc);
                   string(buffer);
       }
      }