Conductive carbon nanotubes (CNTs) obtained by dotting carboxylated CNTs with metal nanocrystals by chemical functional groups, are described, as well as a method for fabricating a pattern or film of the conductive CNTs which involves repeatedly depositing conductive CNTs on a substrate to achieve high surface density. A biosensor is described, in which bioreceptors that bind to target biomolecules are selectively attached to conductive CNTs or a conductive CNT pattern or film. By use of the conductive biosensor, various target biomaterials that bind or react with the bioreceptors can be precisely measured directly or by electrochemical signals at large amounts in one step. Additionally, the biosensor can be used for an electrical detection method capable of providing precise measurement results even with a small amount of source material.