We design a photonic crystal fiber (PCF) biosensor, based on the refractive index, capable of operating in terahertz (THz) region. This structure comprises a dual steering wheel (DSW) shape of large noncircular air–hole structure in the cladding region. This PCF is designed using rectangular structured air holes in core, and they are filled with blood components as analytes. We use the full-vectorial finite-element method to optimize the structural parameters and to characterize the proposed PCF. The simulation results demonstrate a high relative sensitivity for water, cytop, plasma, white blood cells, hemoglobin, red blood cells, sylgard184, biotin–streptavidin, polyacrylamide, and bovine serum albumin. As the practical sensor setup requires connecting a single-mode fiber with that of the PCF, we compute the effective area (Aeff), V-parameter (Veff), spot size (Weff), beam divergence (θ), and dispersion (β2) of the proposed PCF over the wide THz range. We envisage that the proposed fiber may not only be useful for the measurement of various blood components but also for polarization-preserving applications in the THz region.