Executing SQL query with params at SQLite and Xamarin iOS app

I'm following this guide to do a custom query with params using SQLite at Xamarin iOS app:

select * from [Contact] where FirstName = 'Alex'

When I query it using plain string it works fine:

_db.Query<Contact>("select * from [Contact] where FirstName = 'Alex'").ToList();

but I want to execute it using params to avoid injections:

_db.Query<Contact>("select * from [Contact] where FirstName = '?'", "Alex").ToList();

Trace: Executing Query: select * from [Contact] where FirstName = '?' 0: First1

Unfortunately it returns 0 results (while initial query returns the required data).