In Twitter, the @ symbol does not get pronounced and it is NOT a substitute for the word ‘at’ in a sentence or phrase.
It is there to denote someone’s username (which used to be called a handle) and it does not get pronounced when reading a Tweet. Ex. “I really enjoyed the session on @Canva by @TechChef4u! #EdTech” In this example, two users were “mentioned.” Canva, an awesome online design tool, & TechChef4u which is the username created by the ever-creative Lisa Johnson.
This use of the @ symbol is different to its use in an email address which, of course, we do pronounce, as in felix at jacomino dot com.
Back to Twitter... the @ symbol is not a substitute for the word ‘at.’
If you mean to use the word at, write it out. Ex. “I had a great time at @MiamiDevice last month! #PDchat”
Sometimes, new users think “at” when they see the symbol and write something like this, “My little brother is @BurgerKing.” What they are really communicating and what's being read by seasoned Twitter users is “My little brother is Burger King.” So, the correct way to write the tweet would be, “My little brother is at @BurgerKing.” And it is read, “my little brother is at Burger King” Of course, that is if you even want to mention @BurgerKing in the first place. And if your brother has a Twitter account, you could have mentioned him too.