The only person that firmly believes in your startup is you. If you find that your employees or your interns don't ooze of that passion you feel every time you hear your start up name, it's not them. It's you.
They have their own interests. They have their own passions, they have their own dreams. Do not accuse them of lacking passion. I had to work for a whole year at a start up to understand what we were trying to do.
Drop the "We only want to surround ourselves with people who love to work here." Instead, give people a reason to want to work here.