As technology is progressing, nanotechnology is emerging as new field with wide range of possibilities and surprises. As we are going from smaller to smaller, research in this field is keep on pacing and interest is being increased to search out new avenues using various nanomaterials. Out of panoply of nanomaterials carbon nanotubes have niched "hotspot" due to their fantastic optical, electrical and mechanical properties and their enormous applications as biosensors composites, field emission devices, electronic components etc. Carbon nanotubes based biosensors cover major area of its applications. Biomolecules modify electrical properties of carbon nanotubes. This modulation in electrical properties is detected as signal in order to sense a biomolecule. Therefore, understanding the nature of electrical changes after biomolecular interaction is important. In order to study effect of biomolecular interaction on carbon nanotubes we have chosen DNA as a model biomolecule. An extensive study has been carried out in order to understand the nature of electrical changes in carbon nanotubes after binding DNA.