Q: Can I access a selected app from lock screen

I've bought a card reader to use with my iPad to take card payments for my business. Is there any way I can allow access to the payleven app only from lock screen? I don't want to remove the password from my iPad or give my password to the staff if I'm not there.  If not is there a way to provide extra security for my existing apps without losing my stored information so they can't get onto my Facebook or Twitter accounts or worse my internet banking. (For the record I trust my staff but you can never be too careful)