In this paper, we describe a single-wall carbon nanotube (SWNT) based biological sensor for the detection of biomolecules like Streptavidin and IgG. SWNTs have been employed for two types of sensing mechanisms. First, the changes in the electrical conductance of the carbon nanotube (CNT) matrix on noncovalent binding of the biomolecules to the side walls of the CNT and, second, quantification of mass uptake of the matrix on biomolecule incubation are presented. Both sensing mechanisms exhibited consistent and highly sensitive responses. Biomolecular immobilization on the CNT surface was monitored by atomic force microscopy