<p>In this work, a fundamental single-band graphene-based biosensor structure is proposed, where the patterned graphene layer is designed in an octagonal geometry. Based on this configuration, dual-band absorbers are developed by integrating additional ring and plus-shaped resonators. All the proposed sensors share a simple three-layer configuration consisting of a metallic ground plane, a SiO₂ dielectric spacer, and a patterned graphene sheet functionalized by the target analyte. By optimizing the geometrical parameters and tuning the chemical potential and relaxation time of graphene, both the resonance frequencies and absorption intensity can be effectively controlled. The designed structures exhibit near-perfect absorption at their resonance bands and provide a compact and efficient platform for terahertz biosensing applications. The first proposed sensor shows a single absorption peak with 99.88% absorption and demonstrates promising results in detecting breast, cervical, and PC12 cancer cells, with the highest sensitivity of 2.14 THz/RIU observed for PC12 cancer cells. The second proposed sensor has two resonance bands, each exhibiting over 97.5% absorption, and shows notable sensitivity for detecting breast, Jurkat, and PC12 cancer cells, with the highest sensitivity of 4.21 THz/RIU observed for breast cancer at the second band. The third proposed sensor also has two resonance bands with over 98.5% absorption for each band and provides suitable sensitivity for detecting basal, cervical, and MCF-7 cancer cells, with the highest sensitivity of 1.66 THz/RIU observed for cervical cancer at the second band. The proposed technology offers a rapid and economical approach for oncological detection, enabling real-time tracking and tailored therapeutic strategies. All computational analyses were conducted using CST software.</p>