ED201:
I am not sure if I understand it well but I need to make a call to ADC_Handler() withing the loop() to take one 1 us reading. it is a little complicated to understand it right away, I am not so good.
No, ADC_Handler gets called when your conversion is complete, -if you enable the interrupt. You set the speed of the adc in its setup registers. No need to call it within the loop().
I came on the same link as ard's, not quite sure you can do shorter than that.