Ionic 2 LocalNotifications plugin - sound problems

Hello guys, i have problems with LocalNotifications plugin, i can’t enable sound and i am getting this error when i add like this, here is the code:

   text: 'Delayed Notification',
   at: new Date(new Date().getTime() + 3600),
   led: 'FF0000',
   sound: isAndroid ? 'file://sound.mp3': 'file://beep.caf'

And i am getting this error in console. “TypeScript error: /Users/kresimirgalic/Desktop/simplido/app/pages/todo/todos.service.ts(43,20): Error TS2304: Cannot find name ‘isAndroid’.”