How are you planning to keep the biometrics secret and to prevent a user to re-use submitted biometrics for authentication?
Note that everything on-chain is completely public to everybody.
In particular, if a user submits their biometrics to a smart contract, they will be displayed to all users.
You might be able to use SNARK / zero-knowledge for that purpose but current limitations on TEAL do not allow for verification of a SNARK.