Sharp, 21, moved to Glanford Park from the Blades for £100,000 in August 2005, and bagged 32 goals last season to help the Iron win promotion to the Coca-Cola Championship.
The deal will see Blades youngster Jonathan Forte move the other way.
© Copyright PA Sport 2007, All Rights Reserved.
Do YOU want to write for GiveMeSport? Get started today by signing-up and submitting an article HERE: http://gms.to/writeforgms