1. Unless the promise made by your brother to return the money was reduced to writing you cannot recover the same from him. When a money is lent by an individual to another the former can maintain a civil action for recovery only if he is able to prove that the latter was bound to repay it. Law permits recovery of only that sum of money which, by a contract between the lender and borrower, was to be repaid to the former by the latter or any person on behalf of the latter.
2. If you can prove that he was bound to repay the lent amount, either in entirety or a part thereof, feel free to file a lawsuit for recovery of money.