It can be developed like that;
You need to print the public key to the paper's one side. and the private key to other as qr code.
Public key should face the outer (so the buyer/user can load/check balance of it).
When you want to use it; dismantle and reach the priv key
Somebody will put OK public key + BAD private key -- balance check OK, but cannot spent!!
I think best to put private key code only.
But offer an idea.